Author Topic: Building a Division Master and modding my RT  (Read 9375 times)


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Building a Division Master and modding my RT
« on: March 01, 2013, 09:42:28 PM »
This is another of my transfer posts from a couple of years back, so if you see any dating errors, it means my eyes were getting tired from too much proof reading and picture modding. It isn't just a matter of picking it up from one place and posting here.


I decided to go with the full kit of parts.

It was dispatched and delivered in what seemed like record time.

The kit came very well packaged, with most of the loose bits stored inside the very strong and rigid steel outer case that has all the holes pre shaped, drilled or tapped, plus inside, there are all the required studs pre mounted into the case.
One thing I did like was the 'membrane' keyboard sheet. If you use the unit a lot, and wear it away or damage it, on the site you can download the overlay, print it out on a sheet of photo paper, and then laminate it, you have a brand new membrane. I actually used a few extra double sided strips on the back of it, but I am sure what it comes like is completely acceptable.

This is what was stored inside the case, after a load of bubble wrap was removed to expose it all.

Electronic bits came stuck down to an A4 printed sheet, with circuit board location and description against each component. So it was just a matter of taking a bit off the sheet, bending it up and sticking it into the right location holes on the board.

The same sort of sheet but with misc components and fixings.

You can buy ready printed and bound instructions, but I just downloaded the PDF files and did them myself.

So I got together some of my old tools that I used to use in my heyday with electronics.

But before doing anything, I had to prepare the stepper motor and power supply because as you build up the boards, you are required to check for voltages and correct operation. I bought my stepper from Arc Euro, about the cheapest place I have found. In fact I bought almost every extra that I needed from the same place.

The little plastic box had a D shaped cutout put into it, to fit around the rubber grommet on the stepper. The back of the box was covered with strips of VERY hi-grip double sided tape (used to fit outside trim onto cars), and the box was 'stuck' onto the side of the motor.

After trimming all cables to length and getting everything tidied up and into the box, and a small wipe over with petroleum jelly onto the box joints (in an attempt to make it splash proof) the lid was fitted and the kit supplied plug was fitted to the other end of the cable. The stepper was now ready for use.

The power supply was off an auction site for 8 squid, brand new. It needed a new extended output cable and relevent plug fitted.

Now to start the build.

I followed the instruction book to the letter, first by fitting all the switches and LED onto the board, then by using spacers (washers & nuts) under the board, the correct height for the keys was found (the instructions had it spot on), and everything was tightened up. There is a little dodgy bit of soldering to be done, fitting the socket onto the BACK side of the board. The way I did it, to give me a bit more room to work underneath the socket was to push the pins thru the plastic socket until the were level with the bottom on the inside. After soldering up, you can just push the outer plastic down to the correct height above the board.

This is what it looked like from the other side.

A couple of hours steady work and the board was built. During the build, you check the power supply is working correctly, and when it is to this stage, you attach the stepper and take it thru a set of checks. All worked fine, for a while.

This is the other end of the board.

Everything was going great. The box sockets were fitted and the main board fitted into the box.

It was at this stage my physical limitations came into play. As most will know, I have very little gripping power on my right hand (hence the need for this box). I had just put the ribbon cable from the keyboard to the main board, and then my hand decided to let go of the keyboard side of the box. It ripped the socket from the keyboard card and also took off most of the solder pads. Unfixable to someone of my limited physical capabilites. What was I to do?
I sent Lester (the chap who sells the kits) an email stating my plight. The reply was basically, send the boards and ribbon cable to me, and I will see what I can do. Posted to him on Wednesday, got them back today, Friday, all repaired and functioning perfectly, He also told me that I had damaged a pad on the main board and hadn't soldered a pin on the main pic socket, which he duly put right.
So it looks like I am losing a few more faculties as well, my eyesight.
I just cannot believe the help he gave me, and I am sure, if I need anything else from his range of items, I will have no qualms about doing so.

This is the now fully functioning unit.

What do I think of this kit?

Not just because I bought it, I think it is a very simple build, which someone with soldering and working with electronics experience will have no troubles building. My problems with it were caused purely because of my physical limitations.

The second part of this post will be about doing the mods to my RT so that this box can control it.

A bit of machine work at last.

The first part covers modding my RT to put a pair of home made thrust washers into the worm drive system, If you don't want to do this stage, then there is no need to, but I want to remove as much backlash as possible, all in search of that elusive accuracy.

The table came apart in a matter of minutes, the first time it has ever been apart in over 20 years. There was a tiny bit of surface rust inside, but not on any mating surfaces, and the original grease was still on the wormwheel and worm. For a more detailed description about getting this type of RT apart, there is a link on the DM site.

At the bottom of the above page, there is a link to a few more piccies.

The Oilite bearing is the one I was waiting for. The ID is 14mm and the OD 20mm, The length was of no importance other than I needed to be able to part a washer off either end.
The LH bit is the cam action to disengage the worm from the wheel and is also the support bearing for the worm shaft, and the RH item is the worm shaft itself

The first job to be done was to part just over 2mm from either end of the Oilite bush, these will be my thrust washers.
Now a bit about Oilite machining. USE NO LUBE OR COOLANT, it already contains oil and you don't want to contaminate it with anything else. The next bit is most important, DON'T LET IT OVERHEAT, otherwise the oil it contains will turn runny and drip out of the bearing, not what you want to happen. Just take it steady, pecking away and letting it cool, then peck a bit more. My cut, which would normally be over in a few seconds, took me about two minutes for each end.
With it being made of a sintered material, it can easily break if you mishandle it, so take care when deburring.

The two washers were then lapped on the cut face until they measured the same thickness all around the washer. I used 1200 W&D used dry (again no oil or water). One turned out at 2.10mm and the other 2.15MM, perfect for the job in hand. That job took about 10 minutes.

This is a bad shot, I couldn't control my shakes, but what it shows is removing 4mm (roughly the thickness of the two washers added together) from the end that goes into the RT, closest to the worm. After machining this cast iron bearing (wobbling about all over the place because of the centre hole offset, the hole ran perfectly true) it was polished and chamfered on the end by hand while the chuck was turning.

The other end had the remaining 0.25mm taken off, purely because the turned face on the end looked like it had been done with a chisel. Again it was polished and chamfered.
So that was the sleeve done in a matter of minutes.

Now this pic shows a thing that always annoys me.
This is the other end of the shaft from the worm, and when the RT was originally assembled, and the backlash adjusted out by means of a round nut, they just stuffed a couple of steel grub screws into the nut to hold it in place. This is the damage it caused, and it took me ages to actually get the nut off, even after removing the grub screws because the threads were so damaged. All it needed was a tiny slug of brass down in the hole before the grub screws, and the thread would have remained undamaged.
As it was, I had to resort to my thread file to get things somewhere back into shape, and get the original nut to screw back onto the thread, 14mm x 1mm pitch, a metric fine. The round nut won't actually be used during final assembly as I will be making a custom Oldham coupling to replace it, I am trying to keep things as short as possible.

So this is what it will look like on final assembly, except the new Oldham coupling will be fitted.

Someone is bound to notice that I should really have taken a couple of mm's from either end of the sleeve, but I didn't want to do that because it would have meant taking off the boss machined on the small end, which if ever the RT is returned to normal, the division set could not have been used. All it means is that the worm sits 2mm closer to sleeve, and it might even help a little by having an unused bit of worm acting on the wheel.

Now ths is where I change my mind from my previous plan of making my own Oldham coupling end. For two reasons, I had made a balls up of my initial calculations which would mean I would be doing finger gymnastics trying to assemble the coupling and set up for no end float at the same time down the length of a fairly small diameter tube.
The other reason was that when I stripped down to the thrust washers this evening, the wear pattern on the faces was absolutely perfect, so rather than spoiling a good thing, I decided to go with what I had.
So I cut some soft brass slugs from a bit of 2mm rod, ground down a couple of grub screws to the right length. Then it was just a matter of a slug down the hole followed by a grub screw, this will stop damage to the threads, set up the zero end float and tighten things up. It turned out perfect, no detectable end float and the whole lot turned as smooth as the proverbial babies bum.

So that left me going the normal route people would take, just fitting an Oldham coupling to the 12mm handle spigot. My problem, 1" diameter coupling, fine, 10mm bore, not good.

So a spell on the lathe with a boring bar had it opened up to the right size.

I need to mention a little about couplings such as this, especially the ones with this type of clamp system. On no account try to drill them out to size, all the cross cuts will deflect the drill, and the hole could end up almost anywhere. By boring, that problem doesn't occur, and only takes a few minutes anyway. That is a warning that should be followed unless you want to end up with a wobbly coupling.

So everything was to my liking, and it was time to assemble everything into a RT. Just a reverse of the strip down procedure, and I assembled everything with bedway oil, which will also be used during it's machining life, that is why ball oilers are fitted and not grease nipples. But again two little things I did extra.

If you notice the main clamp screw on the casting top, I have knocked the tightening finger pin all the way thru to one side, this makes it much easier to do up/undo, but the screw must be in position before the main table is put on, otherwise you won't be able to screw it into the hole.
The other, is the clamp ring that is screwed onto the end. It has four locating bolts, but also four adjusting screws that are used to remove end play in the spindle assembly to RT. A few minutes spent adjusting those and the locating bolts will get rid of all end play, but still allow smooth rotation of the worm spindle housing.

Just a little mechanical marking out/measuring exercise to find the PCD of the bolt holes in this flange. It will be used when the support tube is made.

So it is now at a stage where a few things need to be made.

First things first, on the last bit, I showed a bit of calculation written down on the undersheet. It said 16 PCD, in fact it should have read 16 PCR (pitch circle radius), so 32 PCD (pitch circle diameter).

I am not completing the RT build up at this time, as it is easier for me to handle as it is.

I now needed to look at fitting the stepper motor to the RT. I am using one that I bought from Arc Euro, so the measurements I will be showing will be for that sized stepper.
First off, I mounted up the 6mm Oldham coupling (the other half of the one I fitted first).

I am trying to keep the coupling tube as short as possible, so I marked up how much needed to be cut off the stepper shaft, a total of 10mm.

A couple of minutes with a hacksaw and his buddy, a file, and things looked just right.

Now I could get things into their correct positions and start to measure up.
The first thing was the OAL of the tube, everything else falls into place around that, and because the width of the stepper and the diameter of the flange on the RT is the same at 56mm, and because I don't have any 56mm square ali bar or larger available, I will be making a 2 part tube, loctited together when everything is lined up.

This is the sketch that I will be using. There are a couple of things that need pointing out.
The first one is that the four corner holes on the flange should read '4 off 5mm tapped holes', plus the data sheet that came with the stepper motor showing dimensions didn't quite match what I was holding in my hand, there was up to 1mm discrepancy in places, especially around the holes area, so I will be waiting until it is all assembled before spotting thru for the four corner holes.

I got another bit made, and it wasn't as straight forwards as I thought it would be. A couple of fixit jobs had to be done, all because I thought I had everything covered.

You know what thought did? He thought he had only farted, but in fact, he had s**t himself.

I thought I had some 60mm ali bar to make this unit out of, but it turned out to be 75mm, and I wasn't going to waste material by having to turn it down that much, so I settled on a smaller piece, that was 2mm under my ideal size. But it won't matter that much.
So the first job was to part it down to rough length.

Following that, faced up to exact length and the spigot end that is going into the flange was turned on the end.

Followed by a 19mm drill all the way thru.

The boring out took a bit of time, but with lots of patience and plenty of lube, I got it to final size.

The now tube was flipped end over, and the 19mm hole was opened out to the required 21mm.
So that was the basic tube made, or so I thought.

It was tried for a rough fit, looks OK.

Then an assembly fit, spot on. I was getting very cocky by now, things were going great.

So just a roughie mark up where the access hole needed to be, and it was time for lunch. Bad move.

So duly fed and watered, I decided to carry on, instead of my usual beauty nap in the afternoon.
Onto the mill with it now, and I hacked a 10mm slot thru to roughly where I had marked it up. It isn't critical, it is only there for guiding the coupling down the tube on assembly and tightening up the grub screw.

This is where I needed my RT, to put the three holes in the bottom, but because it is stripped down, I used the PCD function of my mill DRO for doing it.
So the first thing was to get the hole in the tube centred up with the quill and the DRO zeroed.

This is where things started to go pear shaped.
I was just about to drill the third hole, and then realised I had fed the wrong data into the DRO, and I was drilling on an arc rather than a circle. The second hole I had drilled was way off position.
So all I could do, rather than making a new tube, was to accept the extra hole (it won't be seen), re-enter the correct data and carry on drilling the second and third hole. They ended up in their right places.

After that bodge up, I tried to fit a screw thru one of the holes from the inside. It was then I realised I hadn't allowed for the cap screw heads while boring, and they were catching on the inside of the bored tube, kicking them over at an angle.

So what I did, was to remount the tube back onto the lathe and from about 15mm in, I enlarged the internal bore, so that the screws would fit OK.

This pic shows the duff screw hole, and the enlarged bore.

There is something to be learned here, don't try to machine while you are tired, as I was. Not just for safety's sake, but you can easily make simple calculation mistakes, as I did.

So anyway, things turned out OK in the end. It is now awaiting the flange to be made.

The final part to be made is the stepper mounting flange. I made this out of a bit of 12mm thick ali gauge plate.

First off was to get the top and bottom parallel and to the right size.

Next off I machined one of the untouched sides square to the two finished ones, then it was stood up on that end to have the fourth side brought down to correct size.

This is it showing the four square finished edges.
Because the stepper actually has slightly tapered edges, I made this to a nominal size as shown on the sketch.

The next job was to machine off the anodised surfaces and bring it to 8mm thick using my large flycutter.

After that, I found rough centre, and marked a circle to 1mm under what is required. This will allow me to blitz to this mark, then take it steady after that to bring it to size.

Using a range of drills, most of the excess material was got rid of, much quicker than boring it all the way.

For me, it is easier to bore using my mill, purely because I have a power feed on the Z1 axis.

Even though I only have an Imperial boring head, because I have learned to work in both standards at the same time, I find I can usually get close enough to what is required.

Not bad, only 0.01mm (0.0004") out.
That will be just fine, as the Loctite requires a bit of space to work.

The tube fitted just right, a nice sliding, but not sloppy fit.

The next bit were the four holes for stepper mounting. As I mentioned earlier, the info sheet with the stepper didn't match exactly, so I resorted to manually measuring it.
Because I had made the plate spot on size all ways, it was a dead easy job to use an edge finder on two sides to find the first hole centre, then it was just a matter of moving the plate around, push up to the stop and drill. All holes ended up spot on in line with the ones in the stepper.
It always pays to spend a little more time getting your base sizes correct.

It was exactly the same for when the corners were rounded over, set up the first and the rest follow suit.

The finished mounting plate.

Everything fits OK.

Before I could progress any further, the RT had to be completely built up.
Correct greases and oils used in the right places, and the thrust washer underneath adjusted to give no drag or backlash.

The reason for assembly was so that I could get the just made flange in approximately the right position in conjunction with the tube.
The worm was engaged using the cam arrangement, and the parts marked up before being removed.

Some fast acting, but high shear strength Loctite (clone) was used to join the two pieces together.
I clamped it up in the vice, and left it for a while.

It was rock solid when I got back, but for a belt and braces measure, I drilled and tapped four 4mm holes at the joint between the two. Grub screws with a little more Loctite were inserted, making sure they were below the surface when tightened.
There is no way these two are going to come apart in normal use.

So the assembly was finished off, and the whole lot bolted to the mill table in the normal RT permanent position.
Once everything is fine tuned, I will put a piece of ali metallic tape over the tube access hole, just to stop swarf getting in there.

This is just a quickie demo.

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On the third move, I noticed that the motor strained just momentarily, I think I have the worm a little too tight against the wheel, but if that is all that is wrong, I am very happy with it.

This is just the way I did things. There must be dozens of other ways to mount up the stepper.
Also you would have to take into account the sizes and shapes of the bits you will be trying to join together, so don't follow my actions religiously, you will most probably have to make the sizes to fit what you have got in your hands.

I hope you enjoyed this journey.

Now for another one.

I was asked by a good friend (in fact Peter, HS93, who very recently sadly passed away) 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. He 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.

Peter had just bought himself a Myford lathe, so I said I had an adapter 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 adapter 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, but totally sad because Peter never got to use the full potential of it.

And just to finish off, here is mine being put through it's paces, just to bore you a little more.

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BTW, both of these units should plug directly into a standard 4th axis port on your CNC machine.

Phew   :DrinkPint:


Offline steamer

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Re: Building a Division Master and modding my RT
« Reply #1 on: March 02, 2013, 12:35:20 AM »
Thanks for that John!   I'll be looking into that some time in the future.

"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline ScroungerLee

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Re: Building a Division Master and modding my RT
« Reply #2 on: March 02, 2013, 12:58:40 AM »
Thank you John.  I love to see you take the time to teach us a thing or two.

Mmmmm.... Shiny!


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