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Restoration and upgrade of an old Mini Mill

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sploo

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Yup, it really IS true about "price". With my "budget" (!) one of the things I'm still having to learn (lathe only, me, no mill) is that you really DO need to appreciate how the light-weight components lead to inherent lack of "real" rigidity. But if one isn't in a hurry (what's 4 x 10 mm cuts against 1 x 40 mm cut?) is that it's "only" my time! No real problem, and I don't have the space for "proper" machines anyway. :)
It's probably more true of lathes than mills (as there are quite a few sizes of "home" mills now) but my mini lathe is ~40kg and 80cm long. A lathe that was 1m long and 120kg would be acceptable for a small home shop, have a bit more capacity, and would be much more rigid due to the mass.

The problem is that most of the old lathes for sale are either of the "mini" variety, or north of 1000kg!
 

paulrbarnard

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IRC It's an ER20 collet adapter with an MT3 taper (and importantly, M12 drawbar thread). I also bought a set of imperial and metric ER20 collects. All from banggood.

ER20 only goes up to a maximum of 13mm, so I also bought a 16mm MT3 collet for a cutter I have with a 5/8" shank (though it may be too big for that little mill).

You're lucky with the gears though; I understand they're essentially a "consumable" component. If you're fortunate you break one on the top. If you break the internal gears you're in for a very long day. Given that the internal gears were lunched on my unit I opted to do the belt drive conversion.
I just pulled mine out to check and it is MT3 with 12mm. I just ordered an adaptor and collets from Banggood.
 

sploo

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I started fitting the glass scales...

With the X/Y axes carriage removed, it was a simple job of drilling and tapping holes to fit the scale for the X axis. It's offset to the side to avoid the coolant drain port. The image shows the rear of the carriage:



The small red plastic tabs restrict the range of movement but they're present to help ensure the two parts of the scale are aligned correctly...



...and they're easy to remove once the hole locations are set:



Next it was on to the Z axis. It would have been less work to position the slider of the scale facing to the front, but then the slot in the main body of the slide would be exposed to chips. The left side of the head has an M8 tapped hole that was for the old spring based lifting mechanism (replaced with the gas strut), and an M6 tapped hole would also become available once the (now useless) arrow indicator was removed:



A bit of bodging with some aluminium plate went surprisingly well (other than being very soft and "gummy" to drill), and I needed a couple of spacers (basically thick washers), which were turned on the mini lathe. Then I dropped one. Which of course instantly entered another dimension and could not be found. So I had to machine another 😣:



Bit of a random assortment of screw heads, but it's what I had in the right sizes:



X and Z scales working well; though I've not made any attempts to indicate them in yet:



The Y scale will require a bit of thinking. It would be easy with it the "wrong" way up; but that would definitely get the slider full of chips. I'll have to make another aluminum bracket, but I need to work out how to mount it without fouling the holes to bolt the machine to a worktop or restrict X axis movement.

The sliders do come with aluminium cover plates BTW, but there's not enough space for them on the mini lathe (plus it wouldn't work on the Z axis with the aluminium bracket passing over the top).
 

paulrbarnard

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I started fitting the glass scales...

With the X/Y axes carriage removed, it was a simple job of drilling and tapping holes to fit the scale for the X axis. It's offset to the side to avoid the coolant drain port. The image shows the rear of the carriage:



The small red plastic tabs restrict the range of movement but they're present to help ensure the two parts of the scale are aligned correctly...



...and they're easy to remove once the hole locations are set:



Next it was on to the Z axis. It would have been less work to position the slider of the scale facing to the front, but then the slot in the main body of the slide would be exposed to chips. The left side of the head has an M8 tapped hole that was for the old spring based lifting mechanism (replaced with the gas strut), and an M6 tapped hole would also become available once the (now useless) arrow indicator was removed:



A bit of bodging with some aluminium plate went surprisingly well (other than being very soft and "gummy" to drill), and I needed a couple of spacers (basically thick washers), which were turned on the mini lathe. Then I dropped one. Which of course instantly entered another dimension and could not be found. So I had to machine another 😣:



Bit of a random assortment of screw heads, but it's what I had in the right sizes:



X and Z scales working well; though I've not made any attempts to indicate them in yet:



The Y scale will require a bit of thinking. It would be easy with it the "wrong" way up; but that would definitely get the slider full of chips. I'll have to make another aluminum bracket, but I need to work out how to mount it without fouling the holes to bolt the machine to a worktop or restrict X axis movement.

The sliders do come with aluminium cover plates BTW, but there's not enough space for them on the mini lathe (plus it wouldn't work on the Z axis with the aluminium bracket passing over the top).
You are going to cost me a lot of money. This is now on my list...
 

sploo

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You are going to cost me a lot of money. This is now on my list...
*LOL* Sorry :)

At least based on a quick test you can move the axes accurately to the 0.005mm accuracy (i.e. you can hit an exact value). Whether that little mini mill could actually cut something with 0.005mm accuracy is another matter.

Mostly I want it for accurately drilling hole patterns for motor mounts and other similar jobs, so it should be OK for that.
 

sploo

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It's been more than a month, but I've finally finished the Y axis.

The only way it was going to work was to mount the scale on its side; which also means it's the wrong way up (in the sense that there are recesses for screws, but they're now on the bottom). Flipping it over would have resulted in the cable hanging out of the front:



I modified one of the aluminium covers that came with the scales to shield the gap between the scale and carriage. It removed some of the anodising, but that's just cosmetic:



Next a pair of small spacers were made on the lathe:



Then another bent alum plate to bridge the carriage to the axis:



The handwheel just clears all parts, even with the X axis fully to the right:





In a more normal central position there's plenty of room:



To fix the display I made a couple of small blocks to mount the arm bracket, as the ideal height puts the bracket over my gas strut:



For the moment I've just wrapped the (long) cables round the arm. They could do with reducing, but it'll be a lot of soldering to do all the internal connections, so for the moment I'll see how things go:



 

AES

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Really neat job sploo. Well done Sir.

Of course if I was a nit picker (which I'm not !!!!!!!!) the little ali cover you've made to cover the gap at the carriage COULD have the 2 mounting holes on the vertical face extended slightly into vertical slots - OR have the height of those 2 spacers you made reduced slightly. Either of those would then allow the horizontal face of the bridge to be really horizontal and not slightly tilted backwards.

But that would be REAL nitpicking and as long as the lower edge of that cove doesn't rub against the anodised ali cover below it, no harm done.

(Yup, I'm really being a clever Dick here mate, and just to be clear, in this post my tongue is stuck so far into my cheek that I look even more lop-sided than I usually do). :) Nice job.
 

sploo

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Really neat job sploo. Well done Sir.

Of course if I was a nit picker (which I'm not !!!!!!!!) the little ali cover you've made to cover the gap at the carriage COULD have the 2 mounting holes on the vertical face extended slightly into vertical slots - OR have the height of those 2 spacers you made reduced slightly. Either of those would then allow the horizontal face of the bridge to be really horizontal and not slightly tilted backwards.
If you look at the bottom right of the first image you'll see that the screw holding the scale down protrudes above the side of the scale (because the recess for the mounting screw is on the other side). Unfortunately that means they foul the cover, so I couldn't mount it any lower.

I think I'd get away with the cover being perfectly square as there's just enough clearance under the bridge between the carriage and the axis, but I don't have a sheet metal brake so the ally bending was done... errr... "freehand". But, you know 93 degrees has to be better than 90, as it's bigger, right? 😁
 

AES

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Understood. As said sploo, I really was only pulling ye leg mate (I was just excited 'cos I noticed something - nice pix BTW).

Edit for P.S: I thought that was 89.5 degrees!
 

sploo

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Understood. As said sploo, I really was only pulling ye leg mate (I was just excited 'cos I noticed something - nice pix BTW).

Edit for P.S: I thought that was 89.5 degrees!
I spent a long time swearing at those screws :)

FYI I think the smaller bridge is actually (almost) square. It's the guard that's not in the same postcode 😁
 

AES

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I spent a long time swearing at those screws :)

FYI I think the smaller bridge is actually (almost) square. It's the guard that's not in the same postcode 😁
Yeah, I spotted that (89.5 degrees, just like I said)!!!!!!!!!!!!!

OK mate, I'm going to stop this, I'm just being silly now - really. And seriously now mate, nice job!
 

sploo

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Yeah, I spotted that (89.5 degrees, just like I said)!!!!!!!!!!!!!

OK mate, I'm going to stop this, I'm just being silly now - really. And seriously now mate, nice job!
No worries. I'm pleased to have finally finished it (apart from all the things that still need doing, obviously), but the scale on that last axis is certainly the one that's a bit of a cludge. I'm not pretty either so I'll live with it :)
 

Fergie 307

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Nice job. I have the next size up, an Amadeal 25. Fitted a Chinese two axis kit to it £170 from a guy in Hong Kong on e bay. My machine has a built in dro on the quill. Slightly more room on mine so was able to fit the encoders upright. I was so impressed with the kit I bought another for my Harrison lathe. But a problem in that the large encoders that come with it wouldn't fit neatly on the cross slide. I ended up buying a single slim encoder from Warco for the cross slide. The plug wiring was different so had to rewire it for the correct configuration for it to work with the kits display, both the kit and the Warco slide come with pin out information for the connector so it's easy enough to work it out. Have shortened the cables on both set ups so don't have umpteen feet of extra cable. Even with the extra Warco encoder it was still a lot cheaper than most kits. Both have worked a treat for over two years, and are within the spec as far as accuracy is concerned. I have also fitted a power cross feed to the mill. Looked at the ones sold specifically for it by Grizzly etc. Seem to be a lot of problems with these, and most only seem to give a minimum feed rate of about 80mm/min, not sure what use that is to anyone. After some head scratching I used a unit designed as as Bridgeport type table feed. These are available with a lot to mount them horizontally on the left hand end of the table of my machine, but it's a bit of a bridge up to my mind. I have used a similar idea but with the unit mounted as it were upside down on the right hand end of the table. This means you can mount it so it is level with the table, rather than sticking up above it as in the manufacturer's version. Had to make the brackets and an adaptor to link it to the screw. Massively powerful unit, and with very low gearing, so with it turned right down you can get 10mm/min or less as a minimum feed rate. The other advantage of this type of feed unit is that you can still use the manual wheel without having to have clutches or anything. Many of the aftermarket kits don't allow for that.
 

sploo

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That Amadeal 25 looks nice, but it's a bit rich for me :)

All the bits for the scales and display cost me about £250 (from Banggood). The mill (used, from eBay) was £300, and the gas strut I think was around £30; so ignoring the accessories and small cost of aluminium stock I'm out about £600. Not cheap, but I guess that's a decent price for a small mill with a 3 axis DRO.

I suspect that a power feed will be the next thing I look at - though I've found that a nut driver on a cordless drill works OK as a temporary solution.
 

Fergie 307

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As you say a good price for what you have. I was a bit dubious about the kit, but the seller had good feedback so I thought at that price I would give it a punt. Pleasantly surprised by what turned up. The only thing I didn't like we're the cable ends, which were cheap plastic cased ones. When I shortened the cables I took the opportunity to change them for decent metal ones, they're only a couple of quid each. If you go for the power feed do look at the feed rates. I am sure there are people who would find 80 off mm/min ok. I do a lot in stainless, and sometimes removing quite a lot of material, so like to take it gently out of respect for what is still a relatively small machine. Not sure there would be room to fit the one I have to yours, when I get a moment I will post some pictures. The single Warco scale cost £80, and I can't say was of noticeably better quality than the ones in the kit, either externally or looking at the board inside it. In fairness the Warco did come with a much better assortment of brackets, and the slim scales are always more expensive anyway.
 

sploo

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As you say a good price for what you have. I was a bit dubious about the kit, but the seller had good feedback so I thought at that price I would give it a punt. Pleasantly surprised by what turned up. The only thing I didn't like we're the cable ends, which were cheap plastic cased ones. When I shortened the cables I took the opportunity to change them for decent metal ones, they're only a couple of quid each. If you go for the power feed do look at the feed rates. I am sure there are people who would find 80 off mm/min ok. I do a lot in stainless, and sometimes removing quite a lot of material, so like to take it gently out of respect for what is still a relatively small machine. Not sure there would be room to fit the one I have to yours, when I get a moment I will post some pictures. The single Warco scale cost £80, and I can't say was of noticeably better quality than the ones in the kit, either externally or looking at the board inside it. In fairness the Warco did come with a much better assortment of brackets, and the slim scales are always more expensive anyway.
I did take one of the scales apart to see if I could reverse it for better fitting on the Y axis (no cigar with that design) but I was reasonably pleased with the look of the internals. I strongly suspect the units sold here will be ultimately made in the same Chinese factories anyway.

Given what I've found from the mill so far, it'll need a very low feed rate for anything but aluminium. It makes you realise why the "proper" machines are in the 1 ton+ weight category.
 

Fergie 307

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So this is my power drive setup. Excuse the poor quality of the pictures. The bracket was cut from a section of 125 x 65 steel channel and then machined to remove the fillet inside the angle and give a mounting surface for the unit. The only real grief was making the coupler. It has a blind keyway. I haven't got a broach small enough so ended up grinding down a carbide tipped parting off tool to do it. Otherwise fairly straightforward. The alloy block you can see houses a ball race to support the end of the shaft.
IMG_20210408_121427.jpgIMG_20210408_121221.jpg
 

sploo

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Nice. Is there a clutch, or does it just not mind being back-driven when you use the handwheel at the other end?
 
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