# Similar or very close machines : what differences?



## tino_ale (Jul 21, 2009)

Hi all,

An example :

a Precision Matthew 1236






a model I found in France, LF300/900





The specs are extremely alike. The swing over bed, distance between centers, spindle bore etc are the same. But a few specs are not identical (typo?) like the speed range or the weight for example.

Also on the pictures you can notice how the levers and controls are not exactly the same. If you look closely some parts don't seem to be assembled the same way (like the distance between the three bars in front of the machine).

So, what to think? Are these machines necessarily identical, in what matters? Do they come from the same factory?

Can they have any significant differences, like I don't know, the tolerances in the parts, the bealings quality, how well they are built and assembled, the motor and controller quality... Basically if one is good (which seems to be the case for the PM1236), can the other one be built to a much lower standard.

Why some machines seems to be sold just slightly different under different names, and what should one be aware of and be carefull about. Do they cherry pick the best parts they make for a given brand, use what is left for another less expensive?

Thanks for any input


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## gadget_lover (Jul 21, 2009)

Superficially, The early Prius and the Toyota Echo appeared to be the same. In actuallity, the appearance was driven by the need for streamlining an the ability to carry 4 people.

The same with much equipment. A lathe will have similar controls no matter what the size or who builds it. Many are loose copies of the same venerable designs.

There is no way to judge the quality based on appearance when the hidden internals can be very precise or very cheap. Even the parts you can see can be very different when we need .00005 accuracy.

Daniel


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## precisionworks (Jul 21, 2009)

> can the other one be built to a much lower standard.


Yes it can :naughty:

Quite a few importers use just a few factories in China to produce their machine tools, which gives them a nearly identical appearance. The price difference reflects how much, or how little quality control goes into the machine.

The Precision Matthews lathes are certainly at the high end of Asian lathes. Owners report very few problems with fitment, broken parts, bad motors, etc. This does not happen by accident, but is the result of the importer making the manufacturer adhere to tight QC specs.

Any number of Asian lathes fall at the other end of the spectrum. Little or almost no QC, ill fitted parts, shavings in the gear box, motors that burn up within a few months, etc. But they look almost like the Precision Matthews lathe so they must be about as good, even though the price is lots lower ...

In machine tools, you rarely get more than you pay for. Spend as much as you can, and then some, and you won't have to spend a week or two tearing down, fitting, and putting together something that will never be right.


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## tino_ale (Jul 21, 2009)

Alright that makes it rather clear I guess :sick2: Two import machines can look 99% the same and be wastly different in how good they are.

Actually I am not trying to find a better deal than a Precision Matthew. Thing is I am in France and I not sure if it's doable to buy from the US. I found this lathe and was trying to see how it compares to the PM1236 since it looks so alike. Sadly I could very probably pay twice the US price here for a look-alike built to a much lower standard. I can't see how I could get that information though.

If I were in the US I would not think more and get a PM. When I see you guys get the PM1236 for less then $3K with free shipping heck if the machine is good quality I think it is heck of a good deal.

Thank you for your input


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## BoarHunter (Jul 21, 2009)

As said above, only a few Chinese mfgd for a lot of different brands.
http://www.siegind.com/index.htm
With the move toward CNC and the economic crisis, you can find a lot a good quality second hand machine tools. A 30 years old German, Swiss, Japanese lathe beats all the modern cheap Chinese stuff.
The problem is that usualy the big ones are selling for cheap as they need a proper environment and power.
The workbench models are a bit pricey as many hobbyists compete for them.

Second hand US machine tools are OK too but because of non standard parts, you may have trouble fixing them. If you have to replace the spindle ball bearings, for example, good luck. Even simple bolts are specials.

To import a Chinese lathe from the US is totally worthless, not only because of shipping costs but the fact that many chinese mfgd went to the pain of fitting inch based lead screws.
Note that some just changed the dials and not the lead screw themeselves.
Unless you want to go to the pain to design in inch with all the useless complication and funny non standard tooling.


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## precisionworks (Jul 22, 2009)

> Thing is I am in France and I not sure if it's doable to buy from the US.


Contact Precision Matthews (Matt IIRC), and see if he can have one shipped to France direct from the manufacturer. May be possible or it may not, but certainly worth a phone call or email.


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## wquiles (Jul 22, 2009)

precisionworks said:


> Yes it can :naughty:
> 
> Quite a few importers use just a few factories in China to produce their machine tools, which gives them a nearly identical appearance. The price difference reflects how much, or how little quality control goes into the machine.
> 
> ...



As an owner of a Precision Matthews 12x36 lathe, I can 100% support what Barry said about the quality of the lathe. I have put a lot of use on mine since Dec 2008 when I bought it new (use it almost every single week), and it is working like a champ - no problems whatsoever. I have also keep in touch with a few other folks that have bought a PM 12x36 lathe as well, and we are all very happy with the purchase. I would definitely buy a PM machine again, although now that I have re-arranged my "shop", I would have probably gotten the slightly larger/heavier PM 13x40 instead, but if I had the money, the one to buy is the one Brian (Mirage_Man) got:
http://machinetoolonline.com/PM1340T.html

Will


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## tino_ale (Jul 22, 2009)

Thank you for your help. Sending an email to ask about a delivery here.

Is there any other lathe brand that you have in mind that has a comparable offering as PrecisionMatthew from both quality and price standpoint?


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## tino_ale (Jul 22, 2009)

Thanks for your insight. But as a total newbie to Lathe with no prior experience there is no way I can find, choose and CHECK a used lathe, unless of course someone I can thrust basically do the job for me. I don't know such a person.

About the metric vs. inch lathe, I can't see what difference does it make in actual use, as long as there is a thread chasing dial and both metric+inch threading capability.
If it's just about how the lathe is made "inside", I don't care. If it does make a difference to the end user I definitely need to know what it is.

On the 12x36 Lathe I think the dials have both metric and inch display.



BoarHunter said:


> As said above, only a few Chinese mfgd for a lot of different brands.
> http://www.siegind.com/index.htm
> With the move toward CNC and the economic crisis, you can find a lot a good quality second hand machine tools. A 30 years old German, Swiss, Japanese lathe beats all the modern cheap Chinese stuff.
> The problem is that usualy the big ones are selling for cheap as they need a proper environment and power.
> ...


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## StrikerDown (Jul 22, 2009)

tino_ale said:


> Thanks for your insight. But as a total newbie to Lathe with no prior experience there is no way I can find, choose and CHECK a used lathe, unless of course someone I can thrust basically do the job for me. I don't know such a person.
> 
> About the metric vs. inch lathe, I can't see what difference does it make in actual use, as long as there is a thread chasing dial and both metric+inch threading capability.
> If it's just about how the lathe is made "inside", I don't care. If it does make a difference to the end user I definitely need to know what it is.
> ...




I am not positive but if the lead screw is "inch" you can use the chasing dial for inch threads but not metric, and if the lead screw is metric the chasing dial works for metric threads but not inch. I think that is how it works!


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## BoarHunter (Jul 22, 2009)

tino_ale said:


> Thanks for your insight. But as a total newbie to Lathe with no prior experience there is no way I can find, choose and CHECK a used lathe, unless of course someone I can thrust basically do the job for me. I don't know such a person.
> 
> About the metric vs. inch lathe, I can't see what difference does it make in actual use, as long as there is a thread chasing dial and both metric+inch threading capability.
> If it's just about how the lathe is made "inside", I don't care. If it does make a difference to the end user I definitely need to know what it is.
> ...



OK I see.
Now, to operate these machine tools, a minimum of technical expertise is required. I really suggest you start to read some material and get in touch with a mechanic so he can show you the basics.
And the first thing that is taught is the "internals" of these machines. It greatly helps in understanding how to operate them properly and efficiently.


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## tino_ale (Jul 22, 2009)

Oh this is new to me and definitely a bummer if true. The chasing dial is a GREAT feature IMO and I don't see myself threading without it, especially when threading to a shoulder. Considering the inertia of the chuck, I don't see how one could get close to the shoulder without crashing. I need to be able to disengage the feed yet still be able to make the next pass!

Anyone confirms this?



StrikerDown said:


> I am not positive but if the lead screw is "inch" you can use the chasing dial for inch threads but not metric, and if the lead screw is metric the chasing dial works for metric threads but not inch. I think that is how it works!


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## TranquillityBase (Jul 22, 2009)

tino_ale said:


> Oh this is new to me and definitely a bummer if true. The chasing dial is a GREAT feature IMO and I don't see myself threading without it, especially when threading to a shoulder. Considering the inertia of the chuck, I don't see how one could get close to the shoulder without crashing. I need to be able to disengage the feed yet still be able to make the next pass!
> 
> Anyone confirms this?


StrikerDown has it correct.

Don't need no stinkin' chasing dial, it'll do nothing more than slow you down.


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## tino_ale (Jul 22, 2009)

If you can't disengage the threading feed, how do you thread to a shoulder if your chuck doesn't stop instantly (inertia) ? :thinking:


TranquillityBase said:


> StrikerDown has it correct.
> 
> Don't need no stinkin' chasing dial, it'll do nothing more than slow you down.


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## TranquillityBase (Jul 22, 2009)

tino_ale said:


> If you can't disengage the threading feed, how do you thread to a shoulder if your chuck doesn't stop instantly (inertia) ? :thinking:


Roll out, quick like bunny:sweat: 

*Crash* and *destroy* is part of the learning curve  Learn the technique and you'll see it's much faster than using the dial.


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## gadget_lover (Jul 22, 2009)

tino_ale said:


> If you can't disengage the threading feed, how do you thread to a shoulder if your chuck doesn't stop instantly (inertia) ? :thinking:



I do several things:

Run it as slow as it goes.

I power it off early, and finish the last few turns by moving the chuck by hand.

I pick a spot on the chuck and turn it to the same spot each time. That helps you avoid suddenly taking a big cut as you near the end of the thread.

I do use the threading dial. If i understand the concept, using mark #1 will always line up, metric and imperial. I could be wrong.
* CORRECTION * I was wrong. I set up a test case and examined each pass with a loupe. It works occasionally, but most often the next pass is off somewhat. You sometimes get away with that when the bit cuts the full profile on that pass. The advise to leave the half nuts engaged is correct.


Re: imperial lead screw and metric dials.
When they mix them, you end up with interesting divisions, but that's about it. An imperial leadscrew that will move .100 inches per revolution will show as a 2.254 mm per revolution. This is a hassle if you do not have a DRO, since you do long cuts by counting turns of the crank. 


Daniel


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## BoarHunter (Jul 23, 2009)

Threading dials are OK when the pitch are multiples or submultiples of the leadscrew and usefull for long screws.

For short one, less hassle to just backoff and reverse.

Anyway, no miracle here, one can't learn technology and how to operate machines tools on a forum. It requires lot of reading, learning, understanding, practice with someone knowledgeable etc... 
Takes time, dedication and effort.
And these machines are dangerous too !


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## tino_ale (Jul 23, 2009)

BoarHunter said:


> Threading dials are OK when the pitch are multiples or submultiples of the leadscrew and usefull for long screws.


My understanding is that a threading dial is here to let you disengage and re-engage the threading feed, on the same number on the dial that you disengaged it before, no matter what TPI you are using. Are you saying the same thing?

Without a threading dial, I understand you can re-engage anytime but only if your threading pitch is a multiple of the lead screw pitch. Otherwise you won't get back in the same spot at the previous pass. I am unsure if this can actually work on inch based lathe because you are using TPI which generally translate into non round number in pitch vs. a round number of the lead screw pitch, like 0.1".



BoarHunter said:


> Anyway, no miracle here, one can't learn technology and how to operate machines tools on a forum. It requires lot of reading, learning, understanding, practice with someone knowledgeable etc...
> Takes time, dedication and effort.
> And these machines are dangerous too !


Well I have already learned a lot from reading this forum, some websites and watching some "how to" videos.
Sure enough that can't replace a teacher or a specific training but some here have been there before and are now making chips with a similar training or, should I say, the same lack of proper training.
It's not ideal that's for sure but it's doable.
The safety has been emphasized many times here and I am aware of the danger. Thanks for the heads up on this, I think we can never talk too much about safety.


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## TranquillityBase (Jul 23, 2009)

Threading to a shoulder is not a problem, just roll out at the same point with each pass. Pay close attention to the reference point that you're most comfortable with.


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## gadget_lover (Jul 23, 2009)

I learned by buying small machines, reading a lot (books and web) and trying what I learned. youtube is a great help here, since you can actually see how to do things like facing. 

Some operations are hard to envision at first when the jargon is still unfamiliar. Boring was one of those operations for me. I could only find static pictures of a boring bit against a piece of rotating metal but no idea what planes the bit was moving in. 

Now I know. 

Daniel


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## wquiles (Jul 23, 2009)

TranquillityBase said:


> Threading to a shoulder is not a problem, just roll out at the same point with each pass. Pay close attention to the reference point that you're most comfortable with.



+1. Just last night I was doing just that, while making a spider for my spindle:
https://www.candlepowerforums.com/posts/3023119&postcount=283


Another thing (that I learned from somebody here in the forums) that helps (even more so when doing internal threading where you either have limited visibility or none!) is to use a dial indicator attached by a magnet to the ways that has the point pushing against the carriage. As the threading operation moves the carriage to the left (towards the chuck), you look at the needle and when the needle gets to the "release range", which could be 10-25 mills wide or so, depending on how big your [insert your favorite colorful word for your two main round friends down below] are, you then release the threading lever. With this method you can be very consistent and safe at the same time 

Will


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## tino_ale (Jul 23, 2009)

So, in this method, you are releasing the threading lever. How do you get back in the same position for the next pass?


wquiles said:


> As the threading operation moves the carriage to the left (towards the chuck), you look at the needle and when the needle gets to the "release range", which could be 10-25 mills wide or so, depending on how big your [insert your favorite colorful word for your two main round friends down below] are, you then release the threading lever. With this method you can be very consistent and safe at the same time
> 
> Will


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## wquiles (Jul 23, 2009)

tino_ale said:


> So, in this method, you are releasing the threading lever. How do you get back in the same position for the next pass?



Here is a high level of what I do for cutting internal threads on my re-threaded 1xD mags:

- after cutting a thread, back away cutter (so it does not touch/drag on the threads you just cut)
- position cutter at the start of the threads again (here I also use the dial)
- place cutter back in position, plus about 4-5 more mills deeper than last cut
- watch the thread chasing dial. when it gets back to any solid number (this works for cutting 20 TPI and for many others), firmly press down on the threading lever to engage.
- threading resumes, so watch for the dial again to know when to disconnect
- repeat as necessary ...


Note that when I was cutting metric, I started on number 1 on the threading dial, and always used number 1 for each pass.


You can also leave the threading lever engaged:
- after cutting a thread, turn off the motor at the right point in time (remember that due to inertia it will keep moving/cutting after you cut power)
- while the lever is still engaged, back away the cutter 
- put the machine in reverse, go back to starting point
- move cutter to new depth
- turn on motor
- watch threading dial to know when to stop
- repeat as necessary

Will


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## tino_ale (Jul 23, 2009)

I understand both methods THANKS 

Good to know that if needed you can still use the thread chasing indicator for both imperial and metric threads.

Now all I need is a little, ahem, lots of practice


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## precisionworks (Jul 23, 2009)

> I don't see how one could get close to the shoulder without crashing.


Rule #1 (and #2 and #3) is to always use a relief cut. Then learn to do the threading dance, which involves disengaging the carriage feed & spinning the saddle (and threading tool) backward at the same time. Practice this until you get it down cold, and use back gear - or slowest speed available - when threading.


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## StrikerDown (Jul 23, 2009)

tino_ale said:


> I understand both methods THANKS
> 
> Good to know that if needed you can still use the thread chasing indicator for both imperial and metric threads.


 

I just checked the owners manuals for the PM 14 x 40 and the HF 7 x 10 and both machines have imperial (inch) lead screws and the thread chasing dials are limited to use while cutting imperial threads. The PM 14 x 40 has a chart for metric lead screw machines and states the chart is only for metric threads on machines equiped with metric lead screws. 

The PM can cut metric threads but the chasing dial won't work for getting the cutting tool back in the correct position for subsequent passes.


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## tino_ale (Jul 23, 2009)

Don't know about the PM14x40 but wquiles, who owns the PM12x36 I'm interrested in, told me that the machine's thread chasing dial works for both inch/metric threads.

Only difference is with inch threads you can use any number of the chasing dial whereas with metric threads once you disengaged on a given number of the dial you have to stick with if for the other cuts.

If I get a metric lead screws lathe (which matt from PM just told me it's no problem to order) my guess is it will be the exact way around. With metric threads any number of the dial will do, with inch threads, have to stick to the number you first pick.



StrikerDown said:


> I just checked the owners manuals for the PM 14 x 40 and the HF 7 x 10 and both machines have imperial (inch) lead screws and the thread chasing dials are limited to use while cutting imperial threads. The PM 14 x 40 has a chart for metric lead screw machines and states the chart is only for metric threads on machines equiped with metric lead screws.
> 
> The PM can cut metric threads but the chasing dial won't work for getting the cutting tool back in the correct position for subsequent passes.


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## StrikerDown (Jul 24, 2009)

If will says his machine works that way he should know. I had to check the table for mine and for imperial threads 1 will work for all threads from 4 tpi to 112 tpi. Plus for many of the threads more than just "1" can be used, such as 4,8,&10 tpi can use any number from 1-8, but say 5 tpi you can only use 1, 3, 5, or 7 for half nut engagement. For cutting metric threads on this imperial lead screw machine, with a gear change of course, in no case can the half nut be disengaged and re-engaged and correct alignment be guaranteed, acording to the PM 14 x 40 manual. 

In the same manual it also shows the table for metric lead screw equiped machines cutting metric threads and interestingly it only lists the number 3 or 4 for all of the possible metric threads this machine can cut.

Keep in mind that the manual for the PM 14 x 40 is next to useless!

I am cureous if Will has actually cut metric threads with his 12 x 36 or if he just didn't notice that the manual was showing the numbers (table) for metric thread cutting on a metric lead screw machne. 

With the Chinglish used in my manual it is sometimes real hard to interpret!


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## wquiles (Jul 24, 2009)

StrikerDown said:


> If will says his machine works that way he should know. I had to check the table for mine and for imperial threads 1 will work for all threads from 4 tpi to 112 tpi. Plus for many of the threads more than just "1" can be used, such as 4,8,&10 tpi can use any number from 1-8, but say 5 tpi you can only use 1, 3, 5, or 7 for half nut engagement. For cutting metric threads on this imperial lead screw machine, with a gear change of course, in no case can the half nut be disengaged and re-engaged and correct alignment be guaranteed, acording to the PM 14 x 40 manual.
> 
> In the same manual it also shows the table for metric lead screw equiped machines cutting metric threads and interestingly it only lists the number 3 or 4 for all of the possible metric threads this machine can cut.
> 
> ...



I have already cut 7mm threads, both right handed and left handed - they came out perfect. I had to change two gears in the threading gearbox, and I always used the same number in the threading dial (number 1 in my case).

Will


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## StrikerDown (Jul 24, 2009)

That's great, I wonder how they get the machine to do that, but can't with most/many others.

There you go Tino, looks like the perfect fit for you.

I'm glad I don't usually mess with Metric threads... yet!


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## gadget_lover (Jul 24, 2009)

It might work using position #1 if you always move the carriage back to approximately the same spot then run the lathe till #1 lines up again.

I've done metric threads on my 7x12 that way, and they did fit. Maybe I just got lucky. I'll have to examine the next attempt very closely. 

Daniel


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## precisionworks (Jul 24, 2009)

> if you always move the carriage back to approximately the same spot then run the lathe till #1 lines up again.


The purpose of the thread dial is to realign the tool point with the thread root no matter where the carriage is located. The relative relationship between spindle position & carriage position are locked together by gearing, so the only variable is the point of rotation at which the half nuts clamp on the lead screw. Using a specific number, like number 1, assures that the tool point is always in perfect alignment with the thread root.

A good explanation of how & why is here:

http://www.schsm.org/html/using_the_threading_dial.html


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## StrikerDown (Jul 24, 2009)

Thanks Barry,

Here is an article from the same website that explains how to use an imperial lead screw machine to cut metric threads using the half nut.

When reading it it sort of explains why using the thread chasing dial won't work for most threads when mixing imperial lead screw and metric threads... if I am reading it right.

http://www.schsm.org/html/cutting_metric_threads.html


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## tino_ale (Jul 24, 2009)

Very interresting explanation, thank you.

This mean that only a very limited number of metric threads will be able to work with the inch-based chasing dial. You need to convert the metric pitch to TPI and see if :
- it's an even number (any dial mark is good)
- an odd number (all numbered marks of the dial are good)
- a multiple of 0.5TPI (only opposite numbered marks will work, like 1-3 or 2-4)
- a multiple of 0.25TPI (you then need to pick a numbered mark and stick to it for all cuts).

If the conversion gives a TPI number that is not a multiple of 0.25 TPI, then my understanding is that the chasing dial will NOT work at all.


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## wquiles (Jul 24, 2009)

In my specific case, I am pretty certain that when I did the 7mm bolts (1.5mm or 1.25mm pitch - I don't remember), I did keep the carriage engaged and turned the motor in reverse before making another pass. Now after reading the links I understand why it works - thanks for the links 

Will


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## BoarHunter (Aug 1, 2009)

tino_ale said:


> Very interresting explanation, thank you.
> 
> This mean that only a very limited number of metric threads will be able to work with the inch-based chasing dial. You need to convert the metric pitch to TPI and see if :
> - it's an even number (any dial mark is good)
> ...




??????

Could you give a standard pitch that fits this requirement ?


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## tino_ale (Aug 1, 2009)

BoarHunter said:


> ??????
> 
> Could you give a standard pitch that fits this requirement ?


Google : "pitch TPI converter"
First link
0.8mm = 31.75 TPI. Choosing a numbered mark and sticking to it will work


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## BoarHunter (Aug 1, 2009)

tino_ale said:


> Google : "pitch TPI converter"
> First link
> 0.8mm = 31.75 TPI. Choosing a numbered mark and sticking to it will work



This is not a standard fine thread !
http://www.newmantools.com/tech/threadmf.htm

In fact the most common fine threads for tubes (like flashlights) are 0.75, 1, 1.5, 2 because a very common leadscrew pitch is 6. As these are sub-multiples of 6, no problem to disengage the leadscrew.
Less important with CNC machines.

Deviating from standard is never a good idea. All these explanations about the use of TPI, chasing dial shows how something simple in fact can be confusing.


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## gadget_lover (Aug 1, 2009)

BoarHunter said:


> This is not a standard fine thread !
> http://www.newmantools.com/tech/threadmf.htm



Actually, .8 mm is a standard metric thread. 
http://www.newmantools.com/tech/threadm.htm

Why the big deal about metric VS imperial? Why the big deal about standard metric threads only? One of the advantages of buying a lathe is that you can make parts to fit ANY thread, even if they are not standard. 

For instance, you will probably have trouble finding a 22mm x .08 tap or die, but there might be an instance where you want a large threaded rod that will advance .8 mm with each turn.

There are mechanical reasons to chose a particular thread for a particular use. Virtually no one on this site has the knowledge to pick the perfect fastener without consulting a reference book. The materials, the loads, the thicknesses all come into play. 

Personally, before I chose a thread for a fastener I double check the drills, taps and fasteners that I have on hand. If the stresses are small, then it might not matter if I use a 3, 3.5 4, 5 or 6 mm (or, for that matter, a #8, #10 or #12) screw or bolt.

By all means, if you are in a country that subscribes to ISO, then use that standard. But realize that you may buy a piece of equipment that does not use a standard thread (for a million reasons) and that it's best to be flexible enough to work on whatever comes your way.


Daniel


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## BoarHunter (Aug 2, 2009)

gadget_lover said:


> Actually, .8 mm is a standard metric thread.
> http://www.newmantools.com/tech/threadm.htm
> 
> Why the big deal about metric VS imperial? Why the big deal about standard metric threads only? One of the advantages of buying a lathe is that you can make parts to fit ANY thread, even if they are not standard.
> ...



.8 is not a thread used in the M standard fine ! See the reference !
It is the thread for a M5.

When you have to pick a fastener, you have to select it based on the intended use not the drill, taps on hand.

Easy if you own a standard set. 

From 2 to 12, M2, M3, M4, M5, M6, M8, M10, M12, 8 sets which is not a big deal. No need for UNC, UNF, Witwhorth, BA... 

For drill bits, from 1 to 10 in 0.1 increment and 0.5 increment above, no need for strange fractional, gage, letter bits with illogical increments and overlapping plus you never know their exact size !

Drill before tapping ? 
Easy diam minus pitch, no table required.
M5, 5 - 0.8 = 4.2 mm drill ! Every mechanic knows the pitch of the standard M series.

By sticking to ISO standard, you may indeed cut your tap, drill, fasteners, ball bearing etc... inventory by up to two third.

In case you have to fix non standard fasteners, simply drill and tap to standard, or use Helicoil. 
Once a long time ago, I had a machine where due to vibrations the bolts would loosen, replaced the UNC by M6. Problem solved.

And outside of the US, good luck to find a "letter" drill or a #10 tap or screw.

What is in inch in the chinese lathe, the worldcompany car, motorcycle (not vintage !), bike, Xerox copier, computer, etc..., even the new John Deere or Caterpillar ?

What big companies understood a long time ago and which often saved them, hobbyists can do too.


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## precisionworks (Aug 2, 2009)

> Drill before tapping ?
> Easy diam minus pitch, no table required.



That works for thread cutting taps but not for thread formers. Since formers displace & compress metal, rather than removing it, the hole sizing is slightly larger. In addition, the hole size is different for each class of fit. The following example is for the Balax Thredfloer:

Size 1/4 x 20

Class 2B fit (75% thread) requires .225" hole 

Class 3B fit (65% thread) requires .227" hole

Class 2 fit (55% thread) requires .230" hole

(see page 54 in http://www.balax.com/catalog.pdf )

Add to this that there are lots of twist drills that cut over size, even those that are brand new. For a twist drill to produce a correctly sized hole, the point has to be dead center which produces equal length cutting lips. The cutting lips have to have exactly equal angles, and the relief behind the lips has to be identical. 

High end drill grinders, like the Darex V290 or Lilse 91000 that I use, will produce good bits nearly 100% of the time. Experienced machinists can do the same, after just a few years & a few thousand minutes of practice. If the drill makes an over sized hole, the tap has less metal to work with & produces a sloppy thread fit.


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## BoarHunter (Aug 4, 2009)

precisionworks said:


> That works for thread cutting taps but not for thread formers. Since formers displace & compress metal, rather than removing it, the hole sizing is slightly larger. In addition, the hole size is different for each class of fit. The following example is for the Balax Thredfloer:
> 
> Size 1/4 x 20
> 
> ...



True that thread forming dies are better but for the hobbyist ? May be for sheet metal as the thread will be stronger and no much risk for tap breakage.

To drill to the proper size, I just drill 0.5 smaller, than 1/10 then the correct size. The advantage of having a set by 1/10th.

If the drill makes a really bigger hole, may be it's an inchtric ?  
For ex. masonry drill bits labeled 3/8 10mm are in fact 10 not 9.525 as manufacturer takes a standard size and just label it in inch for the US market.


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