Extending the MF70’s Y axis

The MF70 is a great machine and ideal for a beginner conversion. However, I soon found one limitation – the Y axis is limited to a tiny 48mm. I kind of assumed that the 70 in the name of the mill (and also the separate KT70 compound table) meant 70mm, but it seems not.

Retromaster's Y axis extension

A few people have com across this and developed their own solution – notably Retromaster and preconverted machines from Usovo. Whilst these look good and inspired me, one thing I didn’t like is the way the endstop and stepper motor seemed to hang even further off the machine than with a “normal” conversion. They also require a longer leadscrew. I’ve had a lot of trouble finding a suitable leadscrew replacement that isn’t really expensive. I even tried getting a replacement Y-axis leadscrew from Proxxon; it’s longer and also a right handed thread.

I had an idea for a solution that I thought was a little simpler. Rather than moving the end stops further out, I’d reduce their size so that the table could slide over them. They’d still be used for fixing the end of the leadscrew but no longer stop its travel. Nobody else seems to have done this but as the leadscrew is attached only in the centre of the table it shouldn’t be a problem. Other conversions had proven that stability of the table wouldn’t be affected. It seems I’d fallen into the “trap” that most people do… the first things I mill seem to be parts for my mill! Never mind.

The rear of the Y axis

This was the first piece I did as it was smaller and simpler. It’s milled from 5mm think aluminium and in place of the washer on the standard plastic piece it uses a sealed bearing. The leadscrew diameter is 6mm and the smallest bearing I could find had a 12mm outside diameter and 4mm thickness. Perfect. Following other people’s builds, it’s a standard radial bearing rather than a thrust bearing. For the small load it’s under that should be fine. Note the wooden practice piece; it’s far easier and quicker to check for fit using some easily cut softwood first.

It was the first piece of metal I’d milled and I was running the feed rate a little too high, especially on drilling operations. I managed to break my 1mm mill, but I suppose that’s all part of the learning curve. It was pretty noisy too. I now wear earplugs whilst milling! Fitting this increased my Y axis travel from 48mm to a much improved 68mm! 2cm might not sound like a lot, but it makes all the difference.

One thing I’m not keen on is that the shroud over the Y axis leadscrew no longer fits. This means that all the swarf from milling can stick to the leadscrew and increase wear on the delrin under the table. This will probably lead to increased backlash. I’ve not noticed anyone else with a solution to this – including the professionally converted Usovo machines. Maybe something I’ll just have to live with.

The front of the Y axis

Now this was a more adventurous piece! It seemed sensible to make a similar piece and let the table slide over the front end stop. However, the difference between this and the rear is that teh stepper motors are mounted to it. Even if I created a piece, the two screws used for the diagonally mounted motor would foul the sliding table. Could I perhaps use a smaller NEMA17-sized motor rather than my NEMA23s? No. This would still cause a problem. Some other conversions (Jarkman’s for instance) mounted the motor square rather than diagonally – here the bottom mounts would be fine but the top two even more of a problem. The I hit on the idea of using just the two lower mounts. Whilst it wasn’t supported evenly it looked no worse than some of the extended ones. I had to give it a try.

The piece was milled out of a 15mm think chunk of aluminium. I was being a little overcautious with the feedrates and cut depths now and this took ages! I got very bored standing there with a hoover and a vacuum mount is well overdue. The thickness is for two reason. Firstly I had to cut 8mm off the back at the rear because the mill base sticks out a bit further than the table. Secondly, I wanted a firm mount for the motor (now into 7mm of metal). The bearing is set very deep in the piece. This time I used a bearing that is 13mm OD and 5mm thick. This gave a wide enough hole for part of the original handle to sit in. This is the end result.

The mill now has a theoretical Y axis travel of 91mm. The limiting factor is now actually the distance between the spindle and the back of the mill which is 82mm. Whilst you could move the material 92mm, any piece of the work that would be millable at it’s full positive extend would hit the mill before it ran out of travel. All in all, I’m very happy with the result. I’ll attached the CamBam files for these pieces once I work out how to in WordPress. In the meantime contact me if you’d like a copy. Note that the tolerances are very tight. I decided to try giving the mill a bit more support on its travel so the piece may need a little gentle filing before fitting. Also, the pieces have sharp internal corners and the tool radius means that a little filing will be needed here too.