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Home-brew 120mm rotary table

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arnoldb:
The saga continues... 

16 May 2010 

I'm a lazybones; normally I sleep till 9 or 10 am on a Sunday. That morning I awoke at 6 am with the same feeling of anticipation as a 6 year old on his birthday, and just could not get back to sleep... Once in a rare while I get days like this, and I cherish them; things were going to be good.
 
 When I heard all the neighbours were awake I headed for the shop.
 
 I forgot to turn a groove with a radius of just over 5mm to a depth of 1mm on the rim of the gear blank the previous day.  That was done first - I used a 10mm slot mill to make it, hoping that the tendancy for slot mills to cut slightly bigger than their stated size would do the job. I just cranked the dividing head through 3 full 60 turn revolutions - first infeed cut 0.5mm deep, second as well, and for the third one left as-is to do a final cleanup. Light feeds, as the setup most definitely was not as rigid as one would want:
 
 
 Next I set the whole lot to the needed 4.5 degree angle from horizontal. This meant my center reference to the blank was gone. Measuring things were difficult - well pretty much impossible - but fortunately I did zero the mill on all axes before changing the angle. I was able to calculate the new "center cutting spot" from those with a bit of trigonometry, and dialed in the differences as appropriate. I then spent more time checking that I did indeed change the angle in the correct direction - upwards vs downwards, and that I didn't make a mistake in my calculations. My dividing head is based on a 60 tooth worm, so some calculations and it turned out I needed to stop on every 35th hole on the 42 hole plate to make a 72 tooth gear.
 
 I changed hole plates (rotten luck; of my 2 plates the wrong one was on  :palm: ) and set the index fingers on the DH and started slitting. One round of 0.1 mm deep slits to check:
 
 I even counted the "teeth" to make sure I had 72!
 
 Satisfied with the above, I repeated a full rotation of slits to a depth of 2.5mm:
 
 
 I have 2 slitting saws (And I still do only own these 2 saws!); the 1mm thick one I used above, and a 0.5mm thick one of the same dimensions (brand new; never been used before). When I checked visually with the hob against the slits, I wasn't sure that it would have enough depth to start auto-rotating the blank once I got to hobbing. So I added the second slitting saw to the mandrel - without removing the mandrel from the collet chuck - and then lifted the Z feed by 0.25mm to account for the "new" total thickness of 1.5mm. Then I ran a full revolution again slitting only 1.2mm deep with the thicker combined saw. If you look carefully, you can see the additional cut in the grooves:
 
 
 With the blank now slit, I needed a way to hob it. I have a bunch of old bearings I get from a local auto-electrician for free - and I selected 2 of the same size with a slightly larger ID than the gear blank - but that were still "sort of OK". Then I dug around for more bits and bobs, and once found, I turned a mandrel to suit the bits 'n bobs, gear blank and bearings from some HRS rod.
 
 
 The Bits 'n Bobs mentioned is a block of brown stuff... My metals are too precious to waste on a once-off use like this, so wood it will be. With the 4-jaw still occupied by the table-in-making, the wood "jumped" onto the face plate after some persuasion. I then started boring out a pocket to fit a bearing in - after center drilling and drilling a 6mm hole right through the block:
 
 
 Once done, I flipped it around, and used the mentioned drilled hole to set the block on center again and re-attached it to the face plate:
 
 
 I then bored a pocket for the other bearing, and also cleared out the center bit to allow the mandrel to pass through:
 
 
 "Gotcha!"s and notes at this point...
 1: A note: I made the mandrel so that it would pre-load the bearings while tightening down the gear blank on its end. I don't have a picture, but if anybody wants one, I'll be happy to make up a quick C-o-C of what I mean.
 2: A Gotcha: When I drilled clearance for the center hole in the wood block, I forgot to make it big enough to clear the bearings' inner races. When I fit everything together and tightened up to pre-load, everything froze up. I ended up fashioning clearance for the inner races with the Dremel and a smallish routing bit. (Too much work to re-setup everything on the face plate!)
 3: Another Note - the method I used is to make this "jig" is VERY crude; it worked for me - I think primarily because I did take the time to make sure both faces of the wood block were parallel, and one side (that was then marked as a reference side) was square to the faces.
 4: A Gotcha: Cleaning wood chips off a well-oiled lathe is a bugger  :lol:
 
 I then clamped the wood block with bearings et al on the mill, standing on the mentioned "reference" side. then with the hob in a collet, I advanced on the Y axis, turning the mill chuck by hand until I could see that everything would mesh, and the blank would auto-rotate. Then I set the mill to it's slowest speed, held my breath and started up. I nearly fainted from holding that breath; things were going really slowly, but the wheel started revolving, and bits of swarf started appearing. I made a mark on the blank with a permanent marker so I could judge progress around, and I slowly started feeding in 0.1mm for every revolution of the blank. after about 5 passes, I stopped, selected the next higher speed on the mill, and started off again; a bit quicker:
 
 
 I can scarcely describe the feeling of immense gratification (and joy!) of the proper profile slowly appearing on that wheel  :ddb: :ddb:
 The end result - fresh off the mill:
 
 Sorry; the photo is a bit out of focus; its pretty hard to try and take a photo of this!. As you can see, the profile is slightly offset to the right -but it will do for me for now.
 
 The worm meshes with the wheel beyond my expectations:
 
 
 I then chamfered the edges of the wheel:
 
 
 Another note: From the above I obviously gashed the teeth too deeply with the slitting saw, but that was the only way I could ensure proper meshing for auto-rotation. I think this can be eliminated by using a much smaller slitting saw - or even better, a little cutter made up to the same OD as the hob with some taper on it's edges.
 
 Having said that though; I'm over the moon - I've never ever made a gear (That was back in May 2010 Remember!), and for a first foray into gear cutting, this came out MUCH better than I expected - especially for a worm & wheel setup   :ddb: :ddb: :ddb:    (Can anyone tell I'm happy  :D )



Back to the here and now of August 2012 - I edited the above smileys slightly to fit with MadModder's ones.  This day 2+ years ago still ranks as one of my all-time favourite and most enjoyable days in the shop; in fact, I can remember it like it was yesterday!! :ddb: :ddb: :ddb:

 :beer: , Arnold

Rob.Wilson:
 :clap: :clap: :clap: :clap: you sure  made a cracking job of making the worm,wheel and hob Arnold  :thumbup:


Rob

ksor:
Surely a very, very nice peace of work  :jaw: :bugeye: !

I wonder if I can do that when I start up my project again ! :scratch:

Thumbs up  :thumbup:

arnoldb:
Rob, Cheers mate  :beer:

 :beer: Thanks Keld, I'm sure you could do it!

17 May 2010

Today's little bit is pretty boring. I milled three small flats on the gear flange and drilled and tapped in those for 4mm grub screws. Then I turned down the end of the shaft for a nice slide fit for the bore in the gear wheel, and milled flats on the turned down section for the grub screws to tighten up on:
 
 With the dividing head still mounted on the mill this was a breeze. I'll make a dedicated mounting for it at some stage though; as the setup is far from rigid enough for serious work on steel - and I have quite a couple of future projects lined up that will require some gear-making.
 
 Everything so far assembled for a look-see:
 
 A bit of a revelation to me as well; the ideas I had for making the worm shaft adjustable just went down the drain; not enough clearance, so it's back to a bit of head scratching. And people wonder why I'm going bald...  :lol: At least it makes cleaning chips out of the hair easier  :D - life always have a positive side!



18 May 2010

When I got home after work, I had a good look at what I have already, and an eccentric will work a treat. The gear height is adjustable - so that's not a problem; if it needs to move closer to the table top I can counter bore its face to clear the bearing pretension nut. Just some fine detail to finish off in my noggin - mostly related to the vernier scale I want on the assembly. As I'll need to turn an eccentric soon, it's time to get the table off the 4-jaw chuck. But this is no time to rush. I thought things through, and decided to graduate the table first; everything was set up ideally already; easy 72 divisions on the dividing head to mark 10 and 5 degree divisions on the table.
 
 I haven't made a spindle lock for my mill yet, so I opted to cut the division markings rather than broach them like Dean did. Darn; all my suitable toolbits have square shanks... So first, a tool was needed. Some 10mm silver steel, a 4mm cross-drilled hole through at a slight angle (not needed here, but possibly in future) and drill & tap the end for a 4mm grub screw. A short length off the 4mm round HSS sticks I keep around; a bit of grinding, and the result:
 
 
 On to the mill - with the cutter set dead on center. I fed Y till the cutter tip just touched against the side of the table, and then moved the workpiece away on X. Another 0.2mm feed on Y and then I started cutting the first 10 degree graduation. Just deep enough in on X till it looked good to me, then I set the mill table stop to stop there. Then it was turn the DH, feed X to the stop & back out; repeat till all the 10 degree marks were done:
 
 
 And after repeating for the 5 degree marks on a shorter X feed:
 



20 May 2010

I finally got the table off the four jaw chuck this afternoon, as I could not see any further possible use for keeping it mounted.
 First off was a trip to the band saw to get rid of the excess:
 
 
 Bandsaws being the fairly rough machines that they are - and I've taken some pains to get mine as accurate as possible - the cut will inevitably shift slightly and not be perfectly square - especially in the vertical plane while cutting. I kept a careful look on the work, and when I detected too much of a deflection in cutting lines, I would stop the machine and turn the workpiece. I did this three times, as can be seen from the photo showing the table and the offcut:
 
 The cut took about 15 minutes to complete - but the blade I have on the machine is not exactly new any more and is begging for replacement. The offcut will make a nice cast iron flywheel for a future project  :headbang:
 
 Next it was back to the 4-jaw with the table. I put bits of soda can on the radius of the chuck jaws to prevent marring of the graduation marks. Then I dialed in the table dead on center on the outside body with just a vibration coming off the needle of my best indicator when revolving the chuck. This step is crucial in the long term:
 
 
 I then added a close fitting 16mm "test bar" in the hole I bored initially through the table center. For me this is a length of silver steel that I know is straight; no fancy test equipment in my shop (YET!). I tested run-out on this a good distance away from the table body. This was to make sure that the back of the table is at a precise 90 degree angle to the axis so that I could turn the face completely parallel with the back side:
 
 Fortunately my old 4-jaw is pretty darn accurate on the faces of its jaws, so I did not have to resort to tricky measures to get things sorted; It was less than 0.005 mm out at the distance I measured, and that's fine with me in the environment I have.
 
 I then faced the table repeatedly with very light cuts - just 2.5 thou infeed at a time; I didn't want a sudden heavy cut on the irregular bandsawed surface to knock things out of kilter! Then I bored the center hole out to 20mm diameter to a depth of 5mm - this will become the register for my lathe chuck mounting plate - and chamfered the register hole and internal 16mm step left at a 30 degree angle. This is for easy location of mounting the chuck plate in future, as well as for easy centering of the RT on the mill table with a bit of 16mm rod clamped in the collet chuck. As a final step, I used a sharp-pointed threading bit to turn light alignment rings on the face 10mm apart from each other.
 The assembled lot is starting to look like an RT - with the exception of the glaring blunder on the bottom right hand cap screw counterbore that caused so much heat in the shop a while ago  :) :
 


 :beer: , Arnold

arnoldb:
22 May 2010

I've been doing some CAD work in the eccentric to try and sort out what I would do. Finally, I arrived at the following:
 
 An eccentric/bearing carrier/vernier plate carrier combination thingumyjig that would give me the features I want. You can download a dxf CAD version here
 
 I set off making the eccentric from some HRS rod (in fact, the left over bit that I had the gear wheel mounted on):
 
 
 Some clean-up and a groove parted in as per plan. Not the best of finishes!:
 
 
 Then I bandsawed the excess off, and mounted the workpiece 5mm off-center in the 4-jaw. Then I turned down the body (not really needed, but makes things easier in future) and drilled a hole through and bored a pocket for mounting a bearing:
 
 With the body turned down, it was easy to mount the three-jaw chuck and bore the opposite bearing's pocket. If the body wasn't turned down, this would have meant using the 4-jaw to bore the pocket. It might have been quicker to do this... I thought I took a photo of the finished eccentric, but while downloading the photos from the camera to my PC I saw that I thought wrong  :palm:
 
 I took measurements from the thus far assembled RT to determine the "center" hole position for the worm shaft "as if I was not going to use an eccentric". Then I added in the eccentric factor and the rotational position I wanted it to occupy for "worm engaged" - which should be the same as not using an eccentric. Some trigonometry calculations and I had the center coordinates for drilling and boring the hole in the RT base for the eccentric.
 I marked that, and set up the base on the mill for drilling and boring. After center drilling, and drilling a 7mm hole, I switched to my biggest drill; a 19mm one:
 
 I've used this drill bit in the lathe quite a bit, and the old Myford copes with it at medium back gear speed with some complaining. My 16mm drill press does not; it's lowest speed is too high. The mill utterly surprised me. On it's highest low range speed, it just turned that "little" drill bit - no complaints whatsoever - and at a good feed rate as well!
 
 I still need to make or buy a boring head for the mill. The 19mm hole I had needed to be bored out to 30mm for the eccentric. I used the boring bar I made for the degree markings and another bit of HSS ground to what I thought would be appropriate angles to bore the hole out. Another surprise! I could go at a good depth of cut - in this photo I'm taking 2mm out of the diameter of the hole (1mm DOC) at a slow but steady down-feed:
 
 The hole was bored to a good sliding fit for the eccentric.
 
 To test everything - the moment of truth - I installed one bearing on the eccentric, and with an 8mm drill as "shaft" tested everything. Next two photos show both the locked and unlocked positions:
 
 



23 May 2010

I started on the rest of the worm shaft assembly today. First a quick mark-out on a piece of 8mm silver steel:
 
 
 One end was turned down to 6mm for a length, and a space for thread-runout made with the rear parting tool, then I threaded the section left between the 6mm section and the run-out M8 - today I "cheated" and used a die instead of single-point turning the thread. Then I milled flats on the shaft; one on the 6mm section, another short one that will be the mounting spot for a collar, and the last flat for mounting the worm on:
 
 
 Next I made the collar I mentioned above from a scrap of HRS rod. The small ridge on it's side is so that it will only engage on the inner race of the ball bearing it will be pressing up against:
 
 
 I drilled two 2.5mm holes (tap size for M3) into the eccentric to carry the Zero/Vernier scale plate:
 
 
 Then I cut a 12mm thick disc off some 40mm aluminium rod, faced it both sides and drilled a 16mm hole through it; this will become the Zero/Vernier plate. I then located it on the eccentric's bearing bore with a bit of 16mm rod and marked hole positions for drilling it's mounting holes by twirling the 2.5mm drill through the holes drilled in the eccentric. Then I drilled 3mm holes trough the plate on the marks, and counterbored the holes to 5.5mm to clear M3 cap screw heads. I also turned the end of a standard 8mm nut down to engage a bearing center like the collar I made earlier. Here is the collection of parts to make up the RT drive unit:
 
 
 And all assembled:
 
 The turned down M8 nut and a corresponding lock nut for it is hidden in the zero plate.
 
 Then I marked and drilled a 3.2mm hole from the top of the RT base through into the eccentric hole, and then opened it up part way down to 4.2mm and tapped M5. A short bit of 3.2mm bronze brazing rod to locate in the groove and a cap screw (for now) to tighten it down:
 
 I struggled to get the cap screw shown above into the hole... Until I realised the hole is M5 and the screw M6  :Doh: - An M5 cap screw went in easily  :ddb:
 
 A bottom view with everything assembled - I had to move the worm wheel over about 1mm towards the end of the main shaft to get perfect engagement with the worm:
 
 
 And an "operator's" view:
 
 
 Does it work ? OOOH YES  :ddb: . A light twist on the top screw, and the eccentric is loose to turn without coming out of the frame, and a twist on the vernier plate, and the worm engages with no perceptible backlash or disengages completely. And everything turns as smooth as silk and no lapping has been done yet  :D .

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