# Micro Mill VS Mini Mill



## gadget_lover (May 13, 2005)

Last year I did a lot of research into mini-lathes and mini-mills for my home shop. I had several restrictions to take into account. I have limited room for tools and I have limited ability to lift things due to a bad back. This meant that I would not be buying a 1/2 ton machine.

I ended up with the Harbor Freight 7x10 Minilathe and the *micro*mill. The micro mill is smaller than the more popular minimill.

I've used the micro mill for more than 6 months, and have a few observations to share. First the specs:

ITEM 47158 Price: $279 on sale (every 3 or 4 months)
Motor: 120V, 60 Hz, 1/5 HP; Speeds: 100-2000 RPM; Capacities: drill 25/64'', end mill 25/64'', face mill 3/4''; Max. travel: x-9'', y-4'', z-8-1/2''; Chuck to table clearance: 7-3/4''; Table size: 9-3/8'' x 5-3/8''; Table slot: 1/2'' x 3/8''; Throat depth: 5-1/2''; Swing: 11''; Spindle stroke: 1-3/16''; Spindle taper: MT2; Base size: 10-1/8'' x 9-3/8''; Shipping weight: 103 lbs.

The footprint and the weight made it an appropriate choice for me. I envisioned machining small parts for flashlights. As such, I felt the small table and limited vertical travel would not be a problem.

This machine does not have a tilting head, so you don't have to worry about trueing it up (Tramming). That also means that you need a tilting vice to cut angles accurately. A tilting vice takes up some of that 7.75 inch table clearance.

The mill is stiff enough for milling small parts with pretty good accuracy. I can typically take off .020 to .050 per pass with an end mill when working with aluminium. Finishing passes of a thousandth or so make nice finishes. Like all small shop machines, the adjustments of the gibs and other contact parts make a big difference.

Using the mill is a matter of cranking the head to put the cutting tool within an 1/4 inch of your work, then using the handle to extend the spindle down till it reaches the right cutting depth. You then crank the table left and right, or front to back to cut the area you want to cut. If you are milling more than 1 1/8 inch deep, you have to move the head assembly down when you get to the end of the spindle travel.

I've had no problem finding tooling to fit the MT2 spindle. Once you get the mill holders and collets it uses the same tooling as any other small mill.

The graduations on the feed handles were confusing. The fine feed (down) is marked in .002 increments, the spindle handle is .005 and the x and y (table) feeds are .001. Unlike the minilathe, which is .040 per revolution, the micro mill table is .050 per revolution. This gets confusing if you are alternating between them.

If I were doing it over again, I might look at the mini-mill (ITEM 44991) instead. The extra 50 pounds would buy an extra 6 inches of spindle travel and a larger table. The total chuck to table clearance would be about the same. The mini mill has a motor about 4 times the strength of the micro. The mini also uses the R-8 taper for the spindle which is even more common than the MT2.

Like all small mills, it benefits from a DRO, or even a dial indicator to accurately measure your cuts.

All in all, I've not had any problems with the micro mill. I've made several small parts such as lathe tool holders. I've drilled or milled aluminium, plastics and steel. I've made a spanner from 3/4 inch thick aluminium plate. There's a learning curve as you find out the limits and get used to the controls. After that it's easy to use.

Daniel


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## gadget_lover (May 13, 2005)

By the way, I get the feeling that at some point I'll be looking to upgrade, and would apprciate hearing about other's experiences. Benchtop VS floor sized, mill drill VS knee mill, that kind of thing.

If anyone's had both the Mico and the Mini mill, I'd love to hear the comparison.

Daniel


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## Iron_Man (May 14, 2005)

Bigger is allmost always better. But nomatter what size machine you have you always find a part to make that wont fit in one set up. The longest part I have made was 40 feet on a mill with a 5 foot travel /ubbthreads/images/graemlins/smile.gif

My back is bad also, but I was able to move my 5000 lbs lathe by myself. You learn to be a rigger if you do much of that.

Go and look at used machines if you can, they are much cheaper.

If you get the CNC bug, look at Mach2 software and Gecko drives.

Les


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## idleprocess (May 16, 2005)

I'm not too familair with machinery, but I was distinctly underwhelmed by the Harbor Freight Micro-Mill. Perhaps it was just a fault of a floor sample that had been yanked on by a few dozen kids too many, but it just didn't seem _sturdy_.

The mini-mill looked and felt a great deal more solid. It was also out of the reach of most kids.


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## gadget_lover (May 16, 2005)

The local Harbor Freight store is a terrible place to look at their products. They have the two smaller mills and both are in terrible shape. They are missing parts and everything is loose. They were also older models than what were currently delivered.

Daniel


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## McGizmo (May 16, 2005)

I have a rutland mill/drill and there is slop in the quill(?) that is a major PITA for any plunge cuts or knowing just what the depth of cut is. I have a rotary table for it and a couple indexible collet holders. I have had success to a certain extent getting what I want but the set up and uncertainty of just "where I am" makes me not look forward to milling projects!! I am spoiled by the DRO on my Hardinge now and I have a 5C collet holder (Aloris quick change type) on order now. I plan to use it on the lathe for two axis milling where possible.

I am now fantisizing about one of these . If I had 440V and room in my shop. I would get a good used brigeport with DRO and just be done with it! As it stands, I am not sure what I am lacking more; room or brains! /ubbthreads/images/graemlins/blush.gif


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## tvodrd (May 16, 2005)

Bridgeports come with dual voltage (220/440)3-phase motors, easily rewired. The one at work "threw a rod" (varidrive) last week, after 18 years. ~$550 worth of parts, and we got back up and running today. /ubbthreads/images/graemlins/smile.gif

Larry


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## DSpeck (May 19, 2005)

If you want something to really drool over, look at the Industrial Hobbies website - I desperately want one of those!!! /ubbthreads/images/graemlins/drool.gif /ubbthreads/images/graemlins/drool.gif /ubbthreads/images/graemlins/drool.gif


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## McGizmo (May 19, 2005)

Larry,
I have a phase converter for the Hardinge. It wasn't a trivial expense and I sometimes wonder if the feed wires to my old garage aren't providing warmth and comfort to the mice as is! /ubbthreads/images/graemlins/icon15.gif My main problem is simply physical space!! /ubbthreads/images/graemlins/frown.gif

Cool Doug!! Thanks for the dream fodder!!


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## tvodrd (May 19, 2005)

Don,
My understanding is the latest from Bridgeport/Hardinge and the quality importers like Kent now come with variable frequency AC drives. They are fine with single phase power and a 30A, 220V circuit is good for 5HP. I too am using a 3HP rotary invertor (for the Bridgeport,) and you're right- not a trivial expense! (But having _instant reverse_ is worth it! 

Oh! I am in the process of having a 19/32 plug and bottoming taps ground and matching adjustable die. /ubbthreads/images/graemlins/grin.gif (Also not a trivial expense.) 

Larry


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## gadget_lover (Jul 9, 2005)

For those wondering about the capacities of the Micro Mill, I just finished cutting a dovetailed slot in a steel toolholder for my lathe.

The slot was .200 deep and .825 across. The tool was 1.5 inch wide. The dovetail was 60 degrees.

I was able to cut .200 deep by .010 with a 3/8 inch HSS 2 flute end mill. Feed rate was between .025 and .050 per second. The finish coume out real nice.

Daniel


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## Anglepoise (Jul 9, 2005)

The beautifully thing about our hobby is that we have time. Thus we can, in some cases, have smaller and less rigid equipment ( less $$$ ). Its amazing what can be done in regards to milling with slow feed and small cuts.


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## gadget_lover (Jan 13, 2006)

I was doing some plunge cuts with my micromill and discovered a deficiency in my mill. I don't know if it's normal or just me. I was using an end mill to create a recess for the shoulder of my lathe's compound leadscrew. The compound was suffering from backlash that was visible to _my_ naked eye. That's pretty bad. The leadscrew was bearing against the DRO's shaft and it owuld bind if I did anything to take up the slack. But I degress.

I was making a simple .120 deep pocket in a small piece of aluminum with a 1/2 inch 2 flute center cutting end mill. I'd already drilled the 3/8 inch hole for the shaft. As the mill approached the .100 mark the chatter increased whenever I advanced it more than 1 or 2 thou per second. I have a dial indicator mounted on the mill so I can monitor the quill travel with some precision.

I realized that each time the mill chattered, the quill was moving downward 5 thou or so. I think the sides of the mill were catching and pulling the mill into the aluminum. The play that allowed this was in the "micro feed" mechanism. It has tons of slop in it's engagement mechanism. I don't normally notice it because the return spring normally takes the play out.

I'll be machining a new mechanism when I have a few minutes to spare.

Daniel


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## HarryN (Jan 13, 2006)

Daniel - I keep telling you, we need to do a joint CNC purchase on one with a bit of umph. Forget the mini.  :laughing:


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## wquiles (Jan 13, 2006)

HarryN said:


> Daniel - I keep telling you, we need to do a joint CNC purchase on one with a bit of umph. Forget the mini.  :laughing:


With friends like Harry you better lock up your wallet/Paypal account - he provides too much encouragement to spend "your" money  

Will


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## scott.cr (Jan 13, 2006)

> This machine does not have a tilting head, so you don't have to worry about trueing it up (Tramming).



Actually, you should still tram this mill. But before you do, solidly mount a dial indicator and put the plunger on the table. Cycle the table through its full X and Y travel. The indicator should not budge. If it does, the table has a taper. The first mini mill I purchased from HF had .009" taper, which I had to correct, or optionally shim every workpiece, which was a pain.

You probably already know how to check the tram... but to change it you have to unbolt the column and put a shim under the side to make things perfectly square. Sounds painful, but it's not that bad (maybe 20 mins work).  Of course tramming is only important if you want your parts to cut flat... having a column that's not precisely square will cause the end mill or fly cutter to cut concave.


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## gadget_lover (Jan 14, 2006)

Damn you Scott! I was totally happy with my mill as it was set up, and now you have to go and say that!



(I'm not really upset).


I thought about your post , and you are right. I should have checked it beyond the simple test of milling a flat, reversing the piece and re-milling.


I put the test indicator in the chuck and ran the table in all 4 directions. The x axis is within .00025 (1/2 of a division) over it's full travel.. The Y is within .0005 for the first 3 "slats" of the table. I don't know the correct name of the individual surfaces between the T-nut slots. The last slat appears to be .0015 high. I confirmed that first by setting a parallel across it and shining my EDC under it. There was a sliver of light. Then I measured from the parallel to the table with the parallel across only the first 3 slats and again across all 4 slats. The parallel was definitely off the center slats.

That's not a killer, since I usually have my vice clamped to the second and third slats.

But then I trammed the mill (to check the head was perpendicular to the table's surface) and find that it's off by .0015 over a 2 inch circle. Darn again. I may live with it, since It leaves barely visible tooling marks. On the other hand, It would be nice to get perfect results, ya know? I have no idea what shim will compensate for that alignment. It seems that the 4 inch column base (about even with the table) would have about a 1 to one correlation with the spindle. So I think that a .001 shim under the front of the base would counter about .001 forward tilt where the spindle meets the table.

BTW, is the setup shown in these pictures valid for tramming it? I'm pretty sure that the indicator point will be in the same relationship to the spindle in all directions using this setup. Is that true?







Daniel


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## gadget_lover (Jan 14, 2006)

Ok, It's an hour later. I bit the bullet and slipped a .002 stainless steel shim under the left side of the column. Got it to within .0005 inch.

As a test, I ran a piece of 6061 aluminum (only 1.5 inch across) under a 3.8 inch 2 flute end mill. The first pass I could barely feel the edge of the cut when I ran my fingernail accross it. I ran it one more time with out changing the depth, and the ridge was almost imperceptable. The rainbow pattern was barely visible.

I lapped the aluminum on a piece of well used 600 grit sand paper glued to a block of lucite. The milling marks disappered in only 6 to 10 stokes, leaving a nice satin surface.

Thanks Scott. I may try to dial it in even closer if I pick up some .0001 shim stock.

Daniel


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## scott.cr (Jan 14, 2006)

Oh cool, very cool, I'm glad everything worked out for you.

The way you have the dial indicator mounted looks valid. It's easier to get a reading if you have the indicator further from the quill, but it sounds like your setup is pretty much "dead nuts."

Good luck with that .0001" shim stock. That stuff's practically see-through. If you drop a piece on the floor you may never find it!


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## gadget_lover (Jan 14, 2006)

I hate it when I throw in an extra zero. It's really nothing, yet it changes the whole message!

I meant to type .001 or .0005. I have some shims used in lock work that are in the .001 range. Maybe I should 
look into using one or two of those.

Is it worthwhile to try to get the last .0005 out of it? I think it will probably not be worth it, since there are all sorts of places where slop may come into play.

Thanks Scott.

Daniel


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## scott.cr (Jan 14, 2006)

Most home-shop DIYs consider .001" per inch to be acceptable tram. If you're getting .0005" in (what looks like in the photo to be) a 2" circle you're in real good shape and I personally wouldn't screw with it further.

Indeed you could spend many hours "tightening" up that machine to reduce slop. I have the bigger, clunkier HF mill; it's not listed on HF's site any more, but it's really just an overgrown drill press with an X-Y table and MT2 spindle. I originally had the same mill you have now, but the motor speed control failed (constant full throttle) so when I went to exchange it, all they had was the bigger and cheaper model. Seriously, I think 80% of my home metalworking projects have been to make parts for it. But now it has variable speed control, fine down feed (like yours) and I removed the play from the leadscrews.

I also have the HF 7x10 mini lathe. Perfect for flashlight work, but a little small to do internal threading on the tailcap end of a 3D Maglite body. I'm still on my first flashlight project and what I'll have to do is thread the outside of the Maglite body and make a new tailcap that's internally threaded. (When I'm done I'll post pics. Sooo excited over my new hobby hahaha.)


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## gadget_lover (Jan 15, 2006)

HarryN said:


> Daniel - I keep telling you, we need to do a joint CNC purchase on one with a bit of umph. Forget the mini.  :laughing:





I almost missed this one!

Lets see, $700 for the mill, $700 for the CNC conversion and $70,000 for the house addition that I would need to actually bring the sucker home! *lol*



wquiles said:


> With friends like Harry you better lock up your wallet/Paypal account - he provides too much encouragement to spend "your" money
> 
> Will



Nah, Harry's a good guy. He's just a bit more adventurous than I am. I start small and slowly (oh, so slowly) move up. One of these day's I'll get bigger, better faster.


Daniel


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