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Home-brew 120mm rotary table

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DaveH:
Very nicely done Arnold  :thumbup: :clap: great photo's as usual  :thumbup: :clap:

Coming a long nicely. 
 :beer:
DaveH

doubleboost:
Hi
Arnold
You are making a splendid job of this
It is nice to see machines working properly  :bugeye: :bugeye: :bugeye:
No comment on the welding  :lol: :lol: :lol: :lol:
John

arnoldb:
 :beer: Cheers Dave & John

 :lol: John, no comment IS a comment  :lol:

08 May 2010

Time was spent on something I particularly like - single point threading.
 
 First thing, I decided to make the pre-load nut. I removed the 4-jaw chuck (with table in making et al) from the lathe and put back the 3-jaw with outside jaws. Some 50mm aluminium rod was then turned down to just under 40mm for just long enough to make an 8mm wide nut and allow parting off. Then I drilled it out to 19mm for the same depth (19 mm, as it is my biggest drill):
 
 
 And parted off:
 
 The white liquid is synthetic water soluble oil mixed with water. Normally I would have used methylated spirits on the aluminium, but I ran out. Sometime in the past, I did try this soluble oil on aluminium, but had less-than-satisfactory results on a 20:1 water / oil mixture as recommended for this oil. This is a "new" batch I made up just the other day, and through a fumble, this mix is more like 10:1 - and it worked a treat on the aluminium!
 
 Then I changed back to inside jaws on the chuck, and chucked up the parted off bit of aluminium. It needed to be bored to inside diameter thread size next. I originally intended to thread the nut and shaft M24x1. The change wheels for turning a 40 tpi thread was still mounted from making the Dremel chuck adapter for the mill.
 My thoughts went as follows: "I'm lazy to change the gear train. Would this much finer thread work ?... It would actually work well for the pre-tentioner nut - finer adjustment control and more than adequate grip. PLUS - I can use the thread dial indicator instead of reversing the lathe after each cut." Choice made  :coffee:
 For running a 40 tpi thread with a 60 degree angle, the thread depth would be 12.5 thou - roughly 0.32mm So the Inner diameter of the nut needed to be bored to 24 - (2 * 0.32) = 23.36mm. I bored it to that, and started setting up for threading.
 
 I have a little multi-purpose boring bar I made out of an old carbide tipped tool shank that takes 4mm HSS inserts. I had a 60 degree threading "insert" already, so I put that in. Here I'm setting it to center height using a gauge I made as one of my first lathe tooling projects:
 
 Note that the tip is upside-down. When I do internal threading, I do it with the tip upside down and cutting against the back of the workpiece. This allows me to do normal infeeding, and I can see what's happening in the cut. It's just easier for me  :D
 
 Next I set the toolbit square using a fishtail gauge; the piece of paper is not to hide the swarf below for the camera shot, but to make it easier to see the tool tip relative to the "V" in the gauge. To set the angle like this would be tricky on the workpiece itself, so I used a length of silver steel chucked in the tailstock drill chuck to do it:
 
 
 The toolbit approaching for a cut:
 
 This looks like I'm running at high speed, but actually I was running at the lathes second lowest back-gear speed. I didn't try to take a photo while in the cut; had to mind the leadscrew disengagement lever then.
 
 The finished threads after taking 2 thou cuts per pass, and about 2 passes on the same cross slide setting for the last two to work out the "spring" in the boring bar:
 
 
 I then put the 4-jaw with contents back on the lathe, and turned the threads on the shaft. I was lazy, and just turned the insert bit in the boring bar upright again - that eliminated the need to set up a new toolbit - and turned the external thread on the shaft with it. The only thing I did before turning the thread, was to use the edge of a half-round file to make a thread run-out groove. When approaching final dimensions, I just tested with the nut for final fit. Here the thread is finished and the nut screwed on:
 
 It looks a bit rough in the photo, but actually the nut spins about 1/3 of the length of the thread with a flick of the finger before it stops  :D
 
 Next I did some more work on the nut in the mill. I want to be able to lock that nut in position when fitting the table together, so it needed some method of achieving this. I slit and counterbored it on one side with a 6mm center cutting slot mill to clear the head of an M3 cap screw, then center drilled the bottom of the counter bore, and ran a 2.5mm drill (that's for M3 tapping) right through, and then just drilled 3mm down to the slit for thread clearance. Then the 2.5mm section remaining below the slit was tapped M3 for as deep as my taps would go. I also milled two opposing flats on it for use when tightening it up. I didn't take photos of every step mentioned here; but here are two I did take:
 
 
 
 And finally - where I stopped for for the day, and how the nut will be used:
 



09 May 2010

First thing, I wanted to get the top plate of the base bolted to the frame; I'd marked it out already for the bolt holes, so I just needed a way to make the whole lot stay together for drilling and so on. I sawed two longish strips of 20x5mm flat bar off a length I keep handy for incidental needs such as this. Both strips were drilled for clearance holes for some 6mm cap screws, and then the top plate and frame were bolted together like this:
 
 The bottom strip of plate is through the mounting slots of the base.
 
 Then I clamped the whole lot down square on the mill table; there is a clamp on the hidden side in the other groove of the mill table:
 
 I forgot to put a piece of paper below it....
 
 Then I started drilling all the holes. Even though I had laid out the hole locations, I decided to go for X and Y coordinates using the handwheel calibrations - as each hole had to be center drilled, then tap size, for clearance trough the top plate and finally counterbored for recessing the M5 cap screws I would be using. So I located the edges of the right front corner the primitive way; with a bit of 6mm silver steel chucked and a piece of paper.  Then I started counting turns and reading handwheels while center drilling each hole, and jotting down the figures on a bit of paper. Here all the holes are drilled to tap size (4.2mm):
 
 
 That lot was followed by a 5mm drill just deep enough to provide clearance through the top plate. The heads of the cap screws measured out at 8.4mm in diameter and just below 5mm high, so I used a 9mm mill to counterbore the clearance holes 5mm deep. My advanced lubrication delivery system is the orangey bottle in the right of the photo  :lol: :
 
 
 With all the holes I needed to tap full of swarf from the counter boring, I used a drill chuck with a 4mm drill to manually clean out the holes. Just plonked the lot on its side, and by hand turned the drill in each hole to get the swarf out. Photo without the hand that should be turning:
 
 
 Then I sat down on the bar stool I keep handy (my "working table" is a bit high), and tapped each hole. The 5 mm clearance holes in the top plate are excellent tap guides to keep things square when starting with the first tap, so nothing fancy required as guide. Just manual work  :dremel: . I'm due for a new set of M5 taps though; I could feel these starting to struggle, but they have tapped many tens of holes in the last two years... (Two years later, and I actually still use that same set of taps after many more holes!) All bolted together:
 
 Things went well didn't it  :scratch: - Well NO - If you look carefully at the left hand hole in the top row in the picture, you'll just see the mark where the end mill wandered when the lot came loose on the mill table. Remember I said I didn't add the piece of paper below when clamping ?  :bang: Fortunately I could recover; and another mark on the table to serve as a reminder... I think I can still hear some bad words echoing around the shop; fortunately Shrek was out of earshot!
 
 With the base finally together, I started on the gear. A slightly oversize chunk of the phosphor bronze getting sawn off:
 
 
 Then faced and bored in the 3-jaw:
 
 
 Next a section of the left-overs from that old big bolt was turned down for a press fit in the bore in the PB ring:
 
 
 Then I sawed off the turned section of steel, and dumped it in my freezer on top of some ice for 10 minutes - it was nice and cold then  :D
 It pressed into the ring in the bench vise without too much effort, enough to give a good press fit, but not so much that the PB ring would crack:
 
 
 Some more turning, and I have the makings of a gear:
 
 
 

 :beer: , Arnold

ksor:
Oh - it look so nice !

I am excited to see how you do this gear - because that's what stopped my project  :scratch:

Please document it very carefully  :)

arnoldb:
Thanks Keld  :beer: - I did document making the gear.  Not long now before I'll be able to post that section of the build  :D

 
10 May 2010

 I needed the hob before I could cut the gear, and while making the hob I could just as well make the worm. Attached (Can't Attach Excel files to MadModder posts) is an Excel spreadsheet I set up quickly to do some calculations from information I drew off the Internet. An interesting thing I found was "crowning" of worm wheels to make sure that the worm/wheel combination can stay properly lubricated. The crowning entails cutting the gear teeth with a slightly bigger hob than the worm would be. Just for the heck of it (nothing like learning from testing) I'll be doing this.
 
 There is a good amount of information on gear calculations here on the web, so I won't go into detail except for that my original planning was for a 72 tooth MOD 1 wheel with a 20 degree pressure angle. Screwcutting for MOD 1 is pretty close to 8 TPI - and bliss; my lathe has an 8 TPI leadscrew. 8 TPI calculates back to about MOD 1.01 - so that's fine with me - I'm lazy to set up weird & wonderful combinations on the change wheels, and this is one of the easiest to set up.
 
 First up, I needed a toolbit with the correct shape; a point with a 40 degree included angle; clearance for helix angle, and so on. I marked out an 8mm bit of HSS for the angled tip using a protractor:
 
 
 A couple of minutes (well, about 20) on the bench grinder, and then some manual work on the oilstone, and I ended up with this:
 
 
 In the first of the above photos, you can clearly see the the bottom of the bit is at an angle to the top; not straight down. This is for adequate clearance of the helix angle; I did not calculate that or anything; just ground it on by gut feel. Also, you will notice I didn't touch the top of the toolbit with the grinder or oilstone; the original ink I marked out with is still on there.
 
 A trial run to measure sizes on the worm-in-making from some 16mm silver steel. I added a lot of run-out space at the headstock side, as this is a fairly coarse thread and the space is needed to stop. I also have the topslide set parallel to the work and locked, as I might have to add some additional side-feed with it to make cutting easier if it becomes too difficult. (That's frowned on by screw-cutting purists, but have stood me in good stead on large threads like these in the past):
 
 
 I stopped with the threads half-done for that night. Just jotted down the necessary readings from the dials so I could continue from there when next I had shop time:
 
 And yes, it was slow going; I didn't have space to add tailstock support, so I went in 2.5 thou infeed steps with a repeat pass at the same depth after every 10 thou.
 
 
 
 13 May 2010
 
 I finished off the worm; it was a simple process of finishing of the threading, drilling it through and reaming for an 8mm shaft. I then parted it off at length leaving a shoulder, in which I cross drilled and tapped for an M4 grub screw (set screw). All done:
 
 
 Next I started on the hob - after honing the edges of the toolbit again. The threading process was exactly the same process as for the worm, but the hob is 1mm larger in diameter as I explained in a previous post. I didn't take photos of the threading done on it; except for a close-up of a bit of swarf that came off while I was turning it. Why? - the swarf shows that the toolbit was cutting properly on all sides and the front:
 
 
 Overall Progress at the end of the day:
 
 
 
 
 
 14 May 2010
 
 I milled the cutting teeth into the hob; no fancy setups for indexing; I just judged by eye for indexing, but I took pains to make sure I got the cutting edges dead on center, and triple-checked that I was cutting the teeth for right-hand rotation of the hob when in use.
 
 
 Instead of milling clearance behind the "teeth", I just took a file to it; 5 minutes in all, and I had some clearance behind the teeth all round. I didn't want to take away too much for clearance, as the hob will be used to auto-rotate the gear blank when I eventually get to cut it. I didn't bother de-burring anything either; the heat treatment will get rid of some burrs, and once hardened, I'll give the cutting edges a once-over with the Dremel with a grinding stone to really sharpen them up - and should remove any left over bits of burr. In this photo you can see how I filed clearance to just behind the tips of the teeth - there's a little facet left just on top of the tooth cutting edge that I did not touch with the file:
 
 
 Another view of the "profile" - as one can see, my "by-eye" indexing was not spot on :
 
 
 
 
 
 15 May 2010
 
 I ended up cleaning the worst of the milling burs with a needle file - tooth by tooth  :palm:
 
 The day's bit involved more thinking than working. Like mentioned, I cleaned the milling burrs off the hob, and then hardened it. This is a fairly big bit of metal, so I went outside and heated it with my butane torch (took quite a while to get it to temperature). When I thought it was about right, I heated it some more, to allow me enough time to turn the torch off first and then plunge in the oil bucket. This is for safety - I don't allow any flames (not even a lit cigarette) when I do an oil dunk, as the smoke coming off is potentially very explosive - and yes - I am positioned between a fire extinguisher and the dunk site to allow me to pick up the extinguisher while departing a possible fire. If you have the luxury of choice, rather use water hardening than oil hardening silver steel.
 Once cooled, I carefully hand-ground the cutting faces with the Dremel and a small green grinding wheel. Everything feels nice and sharp, and the burrs are gone completely:
 
 I'm not going to temper the hob; I think it will do just fine on the phosphor bronze wheel as-is.
 
 Next I turned down and bored out the gear blank to size - well on the OD at least. I miscalculated the last feed while boring, and ended up with the hole 0.1mm over size  :bang: Fortunately, I can still compensate for that mistake, as I haven't turned down the shaft yet for mounting the gear:
 
 
 The gear is too small to hold in the chuck for gashing (well, either that or my slitting saws are too big ), so I turned a mandrel for mounting it further away:
 
 The mandrel was turned in my 3-jaw and never removed - the gear blank was just mounted on it, and the chuck taken off the lathe.
 
 Then the thinking started... How was I going to mount my Myford dividing head on the mill  :scratch: The T slots are not compatible, I needed a way to tilt it (rather than tilting the mill head, which I spent a LOT of time recently tramming in) and also get adequate workspace. I ended up choosing my lathe's swiveling vertical slide to mount the DH on - that will allow me to set the angles needed. I set everything loosely in place on the mill table to see if I could get adequate clearances everywhere and be able to cut some chips without running out of travel:
 
 
 The last challenge was mounting the vertical slide to the mill table. I nearly started cutting metal to make new T-nuts and so on, when I noticed the cross-slide extension I made for the lathe about 4 years ago. Some checking followed; and YES! - I can clamp it to the mill table to mount the vertical slide on. The completed assembly looks like the cobbled together solution that it is, but it should work:
 
 
 That's where I stopped; I'll do the gashing when I'm fresh at a later point; lot's of dividing to do.
 
 
 
 More later
  :beer: , Arnold

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