The project that I have been doing since the beginning of March is now done and dusted, and the chappie is over the moon with the results.
It looks like there are at least four patentable items that I have come up with during the build, so when those bits are sorted out legally, sometime later this year, I will do a bit of a post on it.
So now my time is my own, I will get this project back underway now that I can get back into the shop.
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.
http://medw.co.uk/wiki/index.php?page=6inch+Rotary+Table+Conversion+GuideAt 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 over the Christmas period, and turned up a few days ago. 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 misshandle 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 (roughtly 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 grubscrews 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.
Bogs
