# Drilling Delrin fast



## sortafast (Oct 1, 2010)

I have a job I will be continually doing for my father in law making some handles for him. The material (for now) is delrin. I am trying to reduce the amount of time I spent on operations, and on of the longer ops is drilling a 12.5mm (.492") hole in one end of the handle. Is there a better drill to use other than a twist drill? I am currently using the tail stock and have to move it after every part so that I can get the parts in and out easily, so its a real PITA and kills my shoulders as my lathe sits kind of high. Are there any other good options for drilling that would be quicker?

Also, how hard would it be to get a .500" drill ground down to .496". There is a pressfit cap that goes in the bottom, and .008"± pressfit is a bit much and unnecessary IMO. And last time I had to go and go back through with the boring bar to make the fit a little better.


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## gadget_lover (Oct 1, 2010)

I read elsewhere that a spade bit does a good job. I've not tried it, but it sounds reasonable.

If you are mounting it in the lathe only to drill it, a drill press might be a better choice. An appropriate fixture will hold the part for you, and then the drilling action is just pulling the handle. 

Daniel


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## precisionworks (Oct 1, 2010)

> a drill press might be a better choice


+1

Either a mill or a drill press, probably using a 3-jaw lathe chuck mounted to the table.



> how hard would it be to get a .500" drill ground down to .496".


That's pretty difficult :nana: ... 

Set up on the surface grinder might take 15 minutes (using a 5C coffee grinder) as even Hardinge collets don't always center a twist drill dead nuts. They normally need to be bumped, indicated, bumped, indicated, etc, until there is zero TIR. Grinding the drill would take another 5 minutes.

*However* - you will end up with a drill that has no lands, meaning 100% contact between the drill body & the easy to melt material. I make custom sized drills whenever I use a Balax Thredfloer tap, as they use a tap drill size that no one makes. In steel, they squeal like a pig, even with lots of TapMagic.

Most manufacturers will make special sizes, but setup is going to run $200-$300, plus another $20-$30 per drill bit.

.4961" = 12.6mm, which is a common twist drill size, costing about $10 each. 

If you can find a 12.6 mm drill in slow spiral (low helix), that's the ticket.


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## sortafast (Oct 1, 2010)

precisionworks said:


> .4961" = 12.6mm, which is a common twist drill size, costing about $10 each.
> 
> If you can find a 12.6 mm drill in slow spiral (low helix), that's the ticket.



that might just be the ticket. Since I don't get a ton of money from this job, I don't really want to tie too much of it up in crazy set ups or $300 tools since they won't pay for stuff like that. Simple, cheap and fast is the name of the game.


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## Atlascycle (Oct 1, 2010)

Look for a parabolic drill for aluminum. I make some parts in delrin and the same parts in aluminum, bought a parabolic drill and it is awesome in the delrin.



Jason


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## KowShak (Oct 2, 2010)

sortafast said:


> that might just be the ticket. Since I don't get a ton of money from this job, I don't really want to tie too much of it up in crazy set ups or $300 tools since they won't pay for stuff like that. Simple, cheap and fast is the name of the game.


 
12.5mm isn't an uncommon size this side of the atlantic, it might be worth importing some 12.5mm drills from UK / europe if you're bothered about being that little bit closer to size.


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## Lynx_Arc (Oct 2, 2010)

have you tried drilling a smaller hole and then coming back to drill a larger hole?


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## sortafast (Oct 2, 2010)

Lynx_Arc said:


> have you tried drilling a smaller hole and then coming back to drill a larger hole?



I am going for speed, not accuracy. For what this part is, the hole can wander a bit. I just need to drill the hole in one operation and do so in a quick manner so I am not spending hrs and hrs moving the tailstock around and drilling holes and such. Last time I did these, the drill I used was too small and I had to go back through 100 parts and bore them out a bit. Which wasn't terrible, but it added an extra operation. The faster I can do this the more time I can spend doing other things like sleeping and eating. 

I found some 12.6mm drills at J&L, but they are just regular jobber drills. I was hoping to find something that would help evacuate the cut material faster so that its just one quick in and out. I am going to try one of these drills and see if it helps as I think the drill i was using was a little dull and plastic likes a good sharp edge. We shall see.


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## Lynx_Arc (Oct 2, 2010)

sortafast said:


> I am going for speed, not accuracy. For what this part is, the hole can wander a bit. I just need to drill the hole in one operation and do so in a quick manner so I am not spending hrs and hrs moving the tailstock around and drilling holes and such. Last time I did these, the drill I used was too small and I had to go back through 100 parts and bore them out a bit. Which wasn't terrible, but it added an extra operation. The faster I can do this the more time I can spend doing other things like sleeping and eating.
> 
> I found some 12.6mm drills at J&L, but they are just regular jobber drills. I was hoping to find something that would help evacuate the cut material faster so that its just one quick in and out. I am going to try one of these drills and see if it helps as I think the drill i was using was a little dull and plastic likes a good sharp edge. We shall see.



sometimes it is faster to do it in two parts, if you choose the right size of smaller hole and use a drill press your bit you won't have to press as hard as it takes to keep the large hole itself going. With the second hole (larger) the amount of pressure over the smaller area to cut doesn't have to be as much so it should cut faster with less effort. The first hole is sometimes called a pilot hole.


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## 350xfire (Oct 2, 2010)

I have also been told to use soapy water to lube and cool while doing delrin. Delrin has a bad habit of offgassing some really nasty stuff!


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## sortafast (Oct 2, 2010)

Lynx_Arc said:


> sometimes it is faster to do it in two parts, if you choose the right size of smaller hole and use a drill press your bit you won't have to press as hard as it takes to keep the large hole itself going. With the second hole (larger) the amount of pressure over the smaller area to cut doesn't have to be as much so it should cut faster with less effort. The first hole is sometimes called a pilot hole.



that would still take more time than to drill 1 big hole at the final diameter. Besides, delrin cuts like butter. I would do 2 holes if I was doing this in aluminum or steel. I am looking for the simplest and fastest way to do these. A perfectly strait hole is not necessary for this part. Drilling a hole smaller then drilling a 2nd larger is just not going to happen. If I were to do that I would do what I did before and just drill the hole on the lathe and then bore it out.

I am currently doing these on my lathe at about 1000rpm IIRC, maybe it was 2000 i can;t remember. The bit I was using did an ok job, but was undersized and I had to bore it out after the fact (2 ops + set up time for each op is more time than I really want to spend on this). My mill is tiny. It would not be able to run these parts, and I do not have a drill press at present nor do I really have the room for it in my garage.


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## Lynx_Arc (Oct 2, 2010)

If it is soft enough you could try a forstner bit perhaps.


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## precisionworks (Oct 2, 2010)

A good thread from the PM forum: http://www.practicalmachinist.com/vb/general/how-dill-delrin-205254/


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## archer6817j (Oct 3, 2010)

Did you say how deep the hole is? You could try an endmill in the tailstock. I know you aren't supposed to do that...but there are a lot of things you aren't supposed to do. Also, even a .006 press fit is extremely tight. But if that's what you want: 12.5mm/screw machine length/parabolic. Travers


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## precisionworks (Oct 3, 2010)

> even a .006" press fit is extremely tight



Sometimes it is, other times it's not :nana:

Easily deformed materials like Delrin, and to some extent aluminum, are normally drilled under size (as compared to steel). On a Class V Fit in steel, for a .500" shaft, the hole could be as much as .0016" under shaft diameter.

But this isn't steel, and .0060" under sounds about right. I made an aluminum press fit bushing recently for a customer, material was 6061T6. Almost identical sizing - we measured the hole at .5625" and he requested that I make the aluminum part .5665" - .5670"

I delivered the part & watched him install it. Fit was snug but not overly tight. 

If you need an online reference for class of fit, here's the one I use: http://www.engineersedge.com/general_tolerances.htm


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## wquiles (Oct 3, 2010)

precisionworks said:


> ... we measured the hole at .5625" and he requested that I make the aluminum part .5665" - .5670"
> 
> I delivered the part & watched him install it. Fit was snug but not overly tight.



My guess is that the part that was pressed in was not that much larger than the hole, if it was snug, but not overly tight.

If the hole was .5625", that sounds like a "extremely" tight interference fit if the part is 0.004-5" larger, isn't? I don't see how you would assemble that by hand easily


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## precisionworks (Oct 3, 2010)

> "extremely" tight interference fit if the part is 0.004-5" larger, isn't?


Not with aluminum :devil:

Also, it was driven in with a 2# ball pein hammer. Just a few easy taps seated it. The inside was hollow & a pilot went inside the bushing, so it wasn't hurt by the hammering.


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## wquiles (Oct 3, 2010)

precisionworks said:


> Not with aluminum :devil:
> 
> Also, it was driven in with a 2# ball pein hammer. Just a few easy taps seated it. The inside was hollow & a pilot went inside the bushing, so it wasn't hurt by the hammering.



Ahh - there we go. I suspected it could not have been "just" hand pressed. A #2 ball hammer makes a big difference :devil:


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## Torque1st (Oct 3, 2010)

Have you tried a simple woodworking spade drill bit? Those are easy to regrind to the exact size needed.

You can also mount a drill bit in the toolpost with the proper holder.


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## precisionworks (Oct 4, 2010)

> woodworking spade drill bit


+1

That may be the best suggestion yet 

Since just a couple of thousandths need to be removed from each side of the bit, a fine cut file could be used. Plus, with no flutes to clog, the Delrin chips & curls will come out of the hole easily.


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## Atlascycle (Oct 4, 2010)

How deep is the hole?


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## Torque1st (Oct 4, 2010)

Hey, I try to think outside the box occasionally. I think I used a spade bit to drill some delrin but it has been a LOONNNGGGG time ago.

RE:


precisionworks said:


> +1
> 
> That may be the best suggestion yet
> 
> Since just a couple of thousandths need to be removed from each side of the bit, a fine cut file could be used. Plus, with no flutes to clog, the Delrin chips & curls will come out of the hole easily.


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## 1917 (Oct 5, 2010)

You might try setting your drill, endmill, reamer or whatever up in the toolpost. The carriage usually has more travel and can be moved in/out faster.
Maybe try a 7/16 two flute endmill. offset in the tool post just right to get the right i.d.


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## sortafast (Oct 7, 2010)

1917 said:


> You might try setting your drill, endmill, reamer or whatever up in the toolpost. The carriage usually has more travel and can be moved in/out faster.
> Maybe try a 7/16 two flute endmill. offset in the tool post just right to get the right i.d.



thought about that, but set up time might be a bit of a beeyotch. Plus I would probably have to buy another tool post holder. Once set up though, it would be very fast as I wouldn't need to reset the tailstock after every part. 

I might try the spade bit and see what happens. I just worry some about deflection since i have to go between 2-2.5" deep, which is right at the limit of the tail stock.


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## Atlascycle (Oct 7, 2010)

If you cannot find the correct size drill then you might want to see if there are any tool sharpening companys around that can grind the drills to the size that you need and then grind the lands in to them for you, or just grind it under sized after leaving a small section to properly size the hole. 

We have our end mills reground when they are dull and the grind the relief back in them be fore they send them to be recoated.

Jason


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## Torque1st (Oct 8, 2010)

sortafast said:


> I might try the spade bit and see what happens. I just worry some about deflection since i have to go between 2-2.5" deep, which is right at the limit of the tail stock.


One of the advantages of drilling in a lathe is that the stock turns which tends to self center the drill.


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## 1917 (Oct 9, 2010)

sortafast said:


> thought about that, but set up time might be a bit of a beeyotch. Plus I would probably have to buy another tool post holder. Once set up though, it would be very fast as I wouldn't need to reset the tailstock after every part.
> 
> I might try the spade bit and see what happens. I just worry some about deflection since i have to go between 2-2.5" deep, which is right at the limit of the tail stock.




Not sure how it would work with your lathe but you could make a toolpost by mounting a block of steel. Drill and ream it to the size you need using the drill and reamer in the chuck. Center height would be right on. Add a set screw and grind a small flat on your drill/reamer. A lathe can make a nice horizontal mill for some jobs.


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## precisionworks (Oct 9, 2010)

> you could make a toolpost by mounting a block of steel. Drill and ream it to the size you need using the drill and reamer in the chuck.


+1

That's a great idea ... there are three or four of these dedicated posts on the shelf by the lathe for jobs I've run in the past. 

It's really simple to make one. Buy a length of hot rolled steel square stock - 3"x3" works well for small to medium sized drills. The stock can be center drilled in the lathe chuck, but that means less than half is available to hold the tool ... or two mounting holes can be drilled in the mill (one near each edge) which means the post cannot rotate. Much better as the drill gets larger.

I've also welded up a stack of square plates when a larger post was needed for a boring bar holder: 












The goal in making this TP was to hold the 1.75" Pafana (Polish) boring bar. That bar was purchased specifically to bore a ... DELRIN job  The bore depth on the delrin rod stock was too much for little 1" bar, but the 1.75" bar does a nice job. 

The second objective of this TP project was to make it as butt ugly as possible, and all my friends agree that it rivals any TP made by most third world countries :nana::eeew:


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## HarryN (Oct 9, 2010)

One other option, is to get it done on the right tool. (most likely a mill or drill press). Since you don't have room yourself, consider the impact of jobbing out that specific hole in a batch of 50 - 100 to someone else. If this lets you accomplish more of the "other aspects" of the work, and you can at least break even on the arrangement, why not ?

I have done just enough machining to know almost nothing, but I don't expect a spade bit to be stiff enough for the job of going 1/2 in dia x 2.5 in deep. Maybe a bottom cutting end mill with some chip relief ?


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