Hello:

Now that my Unimat 3 is behaving much better, I am undertaking pending tasks, one of them being a replacement for the OEM plastic drive pulley with an aluminium one.

I am practically finished with it, with disk on dimension and only the grooves left to turn.

I have made a copy of the original but with a couple of differences: I left some material on the ouside face of the pulley for future use.

One possibility is to make another (smaller) groove to use if you flip it around and and another is to have where to put something like disk for a Hall sensor.

The thing is that at this point I am at odds on how to go about making the grooves ie: what tool to use given the small space to work in even when using the small OEM tool holder.

This is the only arrangement I could come up with with the tools I have but I don't like it too much as it would have to be finished by hand with a round file.

I'd appreciate an opinion on this.

Thanks in advance.

Best,

JHM

Hello:

I have given thought to changing the pulley system a few times but the cost of it all has kept me back as there is much tooling I still need to purchase.

That and the availability of and low price of reasonably quality belting was a deal breaker.

And then there's my own lack of experience to consider: for me (at this moment) a round PU belt that will slip under excess force means saving a tool, an expensive piece of material or some weak part of my U3 which may end up being a hassle to source or manufacture.

Thanks for your input.

Best,

JHM

Hello:

Availability of quality common 'O' rings locally is very limited in both size and material. And as they are imported, end up being rather expensive for what they are.

I really like the idea of being able to make my own belts from PU belting material practically on the fly and as needed.

Indeed …

But as I have mentioned above, that is a good thing for me at this moment.

It is an interesting idea to be considered: economical / easily made round belting with proportionally more torque. Would not be much of an issue space-wise: the belt cover plastic is in bad shape and will have to be replaced with another solution.

The trick then will be to make them exactly the same size lest one of them slip.

Thank you for your input.

Best,

JHM

Edited By Julius Henry Marx on 23/06/2023 13:57:21

Hello:

Almost there.

All the carbide bits were ⌀ 3.0mm so I cut a 25mm piece of shank from an old 5mm masonry drill bit in bad shape. Not having suitable stock, made a piece of 7mm x 8mm x 55mm on the four jaw from an uneven piece of steel I had around.

The whole thing will fit nicely in the OEM tool holder:

The question now is what form/shape should the bit be to make the groove?

Thanks in advance.

Best,

JHM

Hello:

Done by taking a stepped approach similar to the one suggested.

This is the tool+holder as used. Not the prettiest but it worked as I intended.

Some with better eyesight than what I have may notice that the bit is not at exactly 90° to the holder and that the hole is larger than the bit. Vice moved, milling table clamps are still on the to-do list.

In any case, as the bit was to be registered against the one of the faces of the pulley and a larger hole did not pose a problem, that was that.

The front end of the bit was ground with a slight slant (maybe 10/15°?) but left at ⌀ 5mm to keep the width of the groove constant and parallel / even. Once centered, it was very slowly fed into the piece till I had an almost square ended channel ~ 3.5mm deep, the almost due to the slant and the cutting edge being a bit lower than the centre.

Granted, it is not the most orthodox technique but it worked quite well to start off the groove both parallel and at the right width in just one albeit very long operation.

The use of a 6x6mm straight finishing tool with a large radius tip was the next step to gently sneak up to the desired inner radius and the rest was done by hand with the end of a rat tail file with an end that is ~ 4mm.

Looking back, I could have waited to purchase a round file such as the ones used to sharpen chainsaws. They come in small diameters (5mm/6mm, etc.) and have a spiral cut pattern which will probably work for this job.

I will probably purchase one for when I turn the pulley for the milling head which is also plastic. Curiously enough (or maybe not) Emco decided to manufacture it with a M12x1 mount instead of the 14×1 one used in the U3. 8^°

Right …

Here is the finished product, tested to run evenly and ready to use:

I got the idea of making a M14x1 mounting hole at the rear facing side of the pulley from the steel pulley that is part of the lathe threading attachment (part #150250) which has a small threaded hole.

I have not used it and probably never will: I only have one chaser and I found it very awkward to both mount on the U3. I find the thread cutting attachment (#150200) is much easier to deal with and use.

This mounting hole could be useful for many things, eg: turning long pieces of round stock and keeping it straight by means of a tube screwed into pulley. It would turn along with the pulley and be true with the spindle axis.

A 100/150mm length should not be a problem and stock up to just under 10mm could be turned without the strain that it would put on the chuck jaws if it were just dangling through the other side of the spindle. Stock with smaller diameters could be guided by means of a plug with a hole of the right size at the end of the tube.

That's all.

Thank you very much for your input.

Best,

JHM

Edited By Julius Henry Marx on 24/06/2023 14:06:51

Hello:

Thank you.

Indeed …

Both for the U3 and its inexperienced operator, but also the type of job that will make you think hard on how to beat the odds. eg: fitting the 6×6 tool on the tool holder seemed impossible till realised I could do it after the carriage was inmobilised in place and then proceed with the bottom of the groove.

Believe it or not, I had already seen that project. Neat!

Thanks for your input.

Best,

JHM

Hello:

Thank you very much for your encouraging words.

Best,

JHM