I was asked by a good friend (in fact I offered as well) to convert a small RT to stepper drive, so he could use one of Kwackers controllers with it, very similar to my Division Master.
These are the RT's that are sold by Arc Euro, and are a real nice piece of kit, very well made. My mate wanted to buy one of the ready converted ones from there, but at the time he needed an RT, the converted ones weren't in stock. Hence this is where I got involved.
So I contacted another friend, who does these conversions, and he told me what bearings were required and how to go about it. I didn't follow his instructions to the letter, and also I haven't shown a blow by blow account of how it was done, only to say, that it was fairly easy and if I was able bodied, I could have done it easily in a day.
No deep stripping was required, just remove the operating handle, undo two grub screws on the side of the main block and the worm spindle can be taken out.
The main cast iron sleeve was first shortened on the RH end by the thickness of two thrust bearings, then the centre hole was drilled and reamed to accept the two internally fitted needle roller bearings, which were loctited in place at either end of the hole. I found the easiest way to do those two jobs was to bore out my soft jaws and hold onto the main flange. That made both shortening and drilling/reaming a dead easy job, otherwise you would need to set up in the four jaw to get the thru hole done, as the part behind the flange is offset turned to allow adjustment of the worm engagement.
This picture shows after the bearings were fitted and held together with the special nut.
Unlike the Vertex RT conversion, this one cannot revert back to manual operation at a later date without some shaft rebuilding, purely because, if you look at the left hand side of the spindle, the skinny bit on the end has to be cut off, and a combination nut/Oldham coupling made up to get the drive to the RT.
Once the new coupling end was made, it was tightened up to give no end float, but also be free rotating. Once that state was achieved, a brass slug was dropped down the tapped hole in the side of the coupling followed by a very tight grub screw. That will make sure it doesn't come loose, but also not damage the threads, allowing disassembly if needed.
The motor shaft was shortened by 10mm, done purely to keep the tube as short as possible.
Once things were roughly assembled, the length of the tube can be worked out. The measurement was from the end of the spindle flange nearest the RT to the face of the main motor flange.
The end of the tube you can't see was recessed to the exact width of the spindle flange with a nice tight wringing fit. This end you can see had a recess put in it that was a tightish fit on the spigot on the motor flange.
The flange on the tube wasn't made too big in diameter and was about 4mm thick. The bore down the tube only really need to be big enough so that things don't foul down the inside, I made it about 4mm larger than the coupling OD. The OD of the main part of the tube was 6mm larger than the diameter of the spindle flange. This was all done as a wingit job, made to fit.
This is what it should look like when put together.
The motor now needed to be connected to the main tube.
A square plate was made, 8mm thick and exactly the same size as the motor flange. Once centre was found, it was bored out so that the main hole was about 0.05 larger than the main tube diameter, and the recess was formed to take the flange of the tube, but about 0.1mm shallower than the flange is thick. That will allow the motor to be turned to a nice alignment fit for the wires etc. just by slackening off the four main holding bolts.
How it fits over the tube.
What it looks like roughly assembled.
The flange on the main tube stops the square flange fitting up to the motor, it is when the screws are fitted that clamps it all up rigid.
Here I had drilled and tapped the four mounting holes in the square flange and tightened things up for now.
In the foreground are the bits that are no longer required, handle, scale, 3 nuts, locking key and the bit I had to cut off.
This is where I deviated from the instructions.
If you look at the tube where it sits around the spindle flange, I had drilled and tapped two diametrically opposite holes that penetrated thru the tube wall and into the spindle flange, then inserted two grub screws so that they sat just below the outside surface. I was told to Loctite this joint, but I thought it was a little too permanent if something went wrong with the couplings or bearings. By doing it that way, it can all still come apart relatively easily. Hence the wringing fit, you want no slop in that assembly at all.
My mate has just bought himself a Myford lathe, so I said I had an adaptor that I had made which was a bit of a tight fit for the t-nuts on my RT, but would fit this one perfectly. So he can use his Myford chucks on the RT if he wanted to.
A little finishing off was done to the square flange on the tube, the corners were rounded off to match the motor, and where the pointer was on the body of the RT to show the handle settings, I aligned up the worm gear to give no backlash but still be free running, then engraved a line on the tube in line with the pointer, just so that it can be set back to somewhere near if ever the worm is taken out of mesh.
The chuck adaptor flange was machined thinner and a spigot was left underneath that aligned with a recess in the RT table, so it was just a matter of dropping it on and tightening up the newly made screws and t-nuts, so everything should be spot on centralised.
This is it mechanically finished off fitted with my 80mm four jaw self centring chuck. He doesn't get that as a freebie, for display purposes only.
All that is left for him to do is to connect up the electric string and pump some wiggly amps thru it.
Isn't it nice when things go right for a change?
Bogs
