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Home-brew 120mm rotary table

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arnoldb:
I've been fairly quiet here on MadModder of late, so it's time I contributed a bit again - I bet some members will be annoyed at that  :lol:

This is a re-post of how I built a home-brew rotary table for my mill just over two years ago.  Having used it quite extensively, it still works perfectly well for my needs.  During the posting, I'll add some additional comments coloured red in the form of a review; it's not often one gets to review or re-think a tool or operations after a period of time!  I'll also add a timeline to show how the build progressed.

So off we go !

24 April 2010

Some research turned up bits and pieces of information on RTs, and then I hit gold on DeanW's build of his rotary table - excellently detailed as always by Dean - and the plans available there. Thank you both Dean and Steve  :bow:
 
 My build was based on Dean's, but I adapted some dimensions and methods to the materials and tools I had available, as well as changed some bits to suit my own needs.
 Some of the things I wanted from the RT were:
 1. Use as much material as possible from what I had on hand or could economically obtain
 2. An adapter to take any of my Myford chucks and to do machining securely on it. (This adapter gets used very frequently - in fact it is mounted on the RT 90% of the time)
 3. Adjustment of backlash on the worm drive - and full disengagement of the drive for "quick indexing" (The backlash adjustment works a treat, though I rarely use full disengagement)
 4. Accuracy to 0.1 degrees or better from the hand wheel, with an option to add dividing plates as needed. (I succeeded in getting that to 0.01o)
 5. Compatibility with as much of my existing tooling as I have. (This was a really good decision back then - and has saved me a LOT of time in use :thumbup: )

One thing that I added later in the build was to make the handwheel zero-able - This really should have been included in the above list; it's one of the features I use the most on the RT!

 As I had to make the worm and gear, I decided on a 72 tooth gear; that gives 5 degrees per turn of the hand wheel and should make things easy to use.
(This was also a really good choice!)
 
I sourced and scrounged whatever materials I would need for the build; some I had lying around, and a lot I had to buy. I ended up with: Some bits of 10x60mm flat bar and a bit of 12mm plate for the base, a lump of cast iron for the table, phosphor bronze to make the gear out of, an old bit of bolt for some material to make diverse bits, aluminium for the handwheel, a brand new angular contact bearing, a bit of shaft from a printer with 2 small bearings to salvage for mounting the hand wheel shaft, and some 8mm and 16mm silver steel to make the shaft, worm and gear cutter from:
 
 
 I started on the base; the bit of 12mm plate I had was too big, so I sawed it down in the bandsaw. It was a bit too big for the bandsaw as well; so I started with as much as possible of the plate clamped in the saw vise:
 
 
 Then, when the saw frame bottomed on the plate, I flipped the plate around with less clamped to finish the last bit :
 
 
 The last cut was done in one go, and I ended up with the RT base plate and some left-over bits of 12mm thick plate for other projects:
 
 
 Then I clamped the plate to the mill table with some bits from the clamping kit and supported on two identical bearing outer rings as spacers, and milled three of the four sides square, with the two opposing sides I could get to, to the exact width for the plate (140mm):
 
 
 The last side of the plate was done by adding an additional small clamp on the opposite completed side to keep the plate in position, and then moving the main clamps over to the finished side as well to clamp down properly to mill the last side both square and to dimension.
 
 Fortunately, I could chuck the plate in the 4-jaw on my lathe; this made it easy to face and bore the hole for the bearing. The corners barely cleared the bed while swinging in the head-gap. :
 
 To prevent the corners of the plate from hitting the apron while feeding, I just used the top slide to offset the toolbit enough. The cross slide was pretty close to maximum extension as well!
 
 With the old Myford in medium back gear speed, I started the biggest facing cut I have tried to date. (Back then it was, and still is!) It took a while; very slow infeed at the start with interrupted cuts, and looking at the chips coming off to increase feed rate towards the center. Not a pretty picture, but the "ringy bands" looks worse than they were actually:
 
  :( I think some of those "bands" were caused by lighting a cigarette or two during the facing process  :palm:
 
 Next I center drilled, the plate, and drilled an 8mm hole through it with the lathe running at its second highest speed, followed by a 19mm drill (the biggest I have) in high back gear speed:
 
 
 Then I bored the hole bigger; (from 19mm to 61.97 mm) I started with a cheapy tungsten carbide tipped boring bar and 20 thou (~0.5mm) depths of cut and things went OK until I tried some bigger cuts. At 40 thou cuts things were going well, but then the carbide tip splintered and everything ground to a halt. Not feeling in the mood to try and re-sharpen the tool, and with the hole big enough for my favourite HSS left-hand(that should be right-hand!) turning tool bit to have adequate clearance, I just plonked that in and finished the cut. I intentionally left a 0.5mm thick ridge about 2mm wide at the back.That was to allow the bearing I have to be pre-loaded without the center of it actually rising up and touching the bottom of the table later on :
 
 A test with the bearing showed that the hole was just about the right size for a press fit for the bearing, but with the plate a bit warm from machining, and the bearing cold, I decided to let everything cool down to the same temperature overnight to make sure of the final fit for the bearing.

More to follow.
 :beer: , Arnold

Rob.Wilson:
Hi  :wave: and Welcome to Madmodder  Arnold   :poke:  :lol: :lol: :lol: :lol: :lol:


Rob  :)

arnoldb:
 :lol: :lol: :lol: Cheers Rob  :beer: :lol: :lol: :lol: - see, I just KNEW I'd annoy someone  :lol:

25 April 2010

First thing that morning, I picked up with the bearing fit, and as I thought, it needed some final sizing. With all the bits at the same temperature, the fit for the bearing would have been too tight, and I ended up taking another 0.02mm (a 0.01mm cut) out of the plate. Then the bearing was a nice hand press fit part-way into it's hole; the rest will need a bit of tapping with a hammer:
 
 
 Then I flipped the plate in the chuck - just loosened two adjacent jaws of the chuck, flipped, and tightened down the same jaws, making sure the plate was flush on the chuck teeth with no swarf trapped. There was no need to perfectly re-center it - the last facing was just to get rid of the scale and to make sure the top face was completely parallel with the bottom. As the table will be riding on this surface, I tried to get a better finish - and succeeded:
 
 After getting rid of the scale off the plate, I stopped and honed the cutting bit to get it really nice and sharp, thus the better result. The scale on HRS plate really blunts a HSS cutting bit quickly.
 
 Next, some bits sawn from 60x10mm flat bar to make the sides of the base:
 
 
 I just clamped the whole lot together in the mill vise and fly-cut the sides flat. A milling cutter might have been quicker, but once again, the scale on the plates would have made it blunt in short order. I could (and did - twice) re-sharpen the HSS bit I had in the fly-cutter. I also pushed things a bit hard; you can see the blue chips that came off; had me doing a dance while feeding getting hit by those  :ddb: and a couple of times I saw sparks flying when some bit of "unknown" matter in the scale was encountered:
 
 
 Then with both the longer pieces one-at-a-time, I squared the bandsawed ends down; one end just square, and then moved to the other end and squared , and then down to the 140mm length needed. After initially squaring the second end, I just measured how far it must be machined down (both plates were about 4mm too long at that point) and went down in 1mm steps on the mill hand wheels with the last step the required fraction of a mm on the hand wheel:
 
 That 17mm end mill makes big chips on 1mm cuts and a vigorous feed  :D
 
 End of work that day; the top plate of the base finished, and the "long" parts of the base down to size:
 
 The short sides still needed to be machined to length. Most of the side plates also needed some slot milling in them.
 I'd not made a final decision on whether to bolt everything together, or to weld it together. I was thinking of welding the side-plates together, and bolting the top plate to them to prevent distortion on the top plate...
 
 :beer: , Arnold

DaveH:
Nice start Arnold  :thumbup: :clap: Looks interesting  :clap:
 :beer:
DaveH

arnoldb:
Thanks Dave  :beer: - this was a lot of fun  :D

26 April 2010

I milled both the "short" sides of the base square and to length. As I'd decided on welding the lower part of the base, I thought it prudent to mil the clamp-down slots in these as well, before welding things together. For milling the 10mm slots, I marked and drilled 8mm holes at the ends:
 
 While locating the holes, I set the mill's x-axis stops, which I have not used thus far, to stop on the holes - so I could do incremental cuts and just stop at the ends without looking at the hand wheels. Disappointment; I have not looked closely at the stops supplied with the mill, and thought they were steel, but it turned out it was plastic looking (and feeling!) like steel. Found that out when tightening the first one down; It went kgrrk and cracked on me. Another mill mod chalked up! (I have not used the stops much after this build, and now, 2 years later with a DRO scale installed on the mill in the general area of where the stops were, I don't even miss them.  I just use the DRO to get to dimensions.)
 
 I bought a new 10mm HSS slot mill on Saturday, and set about using it to mill the slots between the holes:
 
 On the first slot, things didn't go entirely to plan though... The milling bit easily chewed out the slot with 2.5mm down feeds on each pass. Then I got greedy; and tried a 3.5mm down feed... No problem for the cutter; it worked happily, but left a much rougher finish on the sides of the slot - that seemed to get worse as I went...
 By the other end of the slot, I could visibly see the slot was a LOT (~1mm) wider than at the start. I did lock the y-axis on the mill, but it shifted. Note to self! - lock down harder and don't get greedy. I ended up with an 11mm slot and rough edges. I smoothed both sides of the slot out with some fine milling cuts to look OK - with a very fine climb-milling pass (0.1mm) on each side - fortunately the clamp-down slots are not crucial in size.
 The slot on the other piece went much better; I wasn't greedy. I'll have an RT with one wider mounting slot. I could have milled the second slot to match the first one, but I'll leave it as is - as a permanent reminder not to be greedy in future  :lol: (I'd completely forgotten about the wider slot! - Aahhh... Memories! - The "don't get greedy rule served me well since.  And so much for serving as a reminder!)
 And another thing, from now on, if I want a slot of "x mm" size, I'll make it with a cutter of "x-1 mm" size and have some clean-up room left! (This has worked very well since :D )
 
 The plates with the slots - with the over-large one on the right-hand:
 
 
 Mock-up of base - some welding required  :zap: :
 




30 April 2010

I welded up the base frame.
 
 First I clamped the bits of the frame together on the bottom of the base top where it would mount. I did this to make sure that the clamping didn't push things out of kilter, and it also allowed me to make final adjustments with a small hammer to get everything lined up as close as possible:
 
 
 Then very carefully shifted the clamped assembly over onto a spare piece of plate to make sure nothing shifted, and put the whole lot down in an open space on the workshop floor for welding together :
 
 
 Four good tack-welds with the stick welder mid-way on the inside of each corner to prevent distortion as much as possible, and then a lot of welding followed. All welded up on the inside corners:
 
 
 Not a pretty sight  :palm: ; I only had 2.5mm welding rods on hand, which were a bit small for this job, and the thick metal seemed to conduct a lot of heat away very quickly while welding, so my little AC welder struggled a bit even on it's maximum current setting. One day, I'll get myself a bigger DC inverter welder (or a MIG  :thumbup: ):
 
  :( To be honest... My welding skills suck and need improvement. (And even to date they do! - haven't gotten that MIG welder either :lol: )

:beer: , Arnold

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