(Edit) - Moderator - I have put this post on this section as it follows Stilldrillins post on a Rotable Plate - its not really a "How Do I?" article but might make more sense here. Please move it if you think it more appropriate elsewhere. (Edit)
I have a 100mm rotary table and a 100mm 3 jaw lathe chuck and have wanted to find some way of mounting the latter on the former. Funds (lack of) do not permit the purchace of a further lathe chuck at this stage.
I read with great interest the earlier build thread by Dave (Stilldrillin) on how he achieved this for his 80mm chuck, but for me, that method would be impossible since there would be no way of picking up on conventional T bolts in the rotary table slots - the 100mm lathe chuck completely covering the table surface. Dave's post is excellent, and gave me a beginning of an idea.
I had been given a 3/4" off-cut "slice" of 100mm cast iron, sawn from off a very large billet, by a local jobbing engineer's business in our little town and wondered how this could possibly be used as a sort of "transfer plate".
I was talking about the problem to Circlip on Skype (my "Guru" - as Bogs has suggested, every apprentice should have one - although I call him my Rabbi - "Teacher"), and he drew me some "highly detailed and dimensioned" freehand plans on the back of an envelope and held them up to the camera, to show a really elegant way of getting the lathe chuck (or lathe faceplate) mountable on the rotary table, using my slice of cast iron as a "low profile" adapter plate.
The build proceeded - thus :-
Mount and skim one side and the outboard rim of the cast iron in the 4 jaw.
The iron was fairly easy to machine with my home - made tipped tool, but unlike the few castings I have previously had experience of machining, when making a Stuart engine, this material produced crystalline granules as it was cut, rather than black graphite type powder. I suspect it is a much harder grade of cast iron.
Just as Bogs has recommended on the earlier thread, I had previously made a "master" locating peg for the rotary table after I bought it - the central hole is not a Morse Taper - just a lower parallel sided hole leading up to a "countersunk" wider counterbore.
The transfer plate would centre on a spigot, machined like the "master - peg" with a countersunk type taper, but continuing above the surface of the table at the wider dimension - approx. 12mm - for 3mm and then continuing as a threaded stud (M8) through the rest of the thickness of the plate.
After facing the first side, the plate was centre drilled, drilled through tapping size for M8, and counter bored for 3mm with a boring bar to finish/bottom, to accept a very close fit from the spigot, and then tapped M8.
I machined the spigot from a length of 1/2"mm steel bar, turning the three sections at one go (concentricity). I screw cut the M8 length and followed it down with a die, opening it as wide as possible for the last few threads at the shoulder to the middle. This allowed me to screw the spigot into the plate, engaging the counter bored hole with the thread getting quite tight. (sorry, no pics of making this item - got too busy to remember).
It finished up thus :-
I could now work on the other face of the plate.
In hind sight, I could (and should) have put up the 3 jaw chuck and held the spigot on the wider section (concentricity) but put it back (turned over) in the 4 jaw, using parallels as jaw packing and clocking the finished (rear) surface and rim that had been machined as close as possible - 0.02mm. run out on face and rim. I was thinking it would be a stronger mounting this way in the 4 jaw for machining quite hard cast iron, but the spigot should have been o.k. with very light cuts.
I faced the other side, and the remainder of the rim, and then cut the register for the 3 jaw chuck/faceplate (all of the necessary dimensions are given in the Arc Eurotrade catalogue)
Like Dave, I was able to get the register to a very close fit, with the chuck embedded on it and holding "no Hands" - but I did put a chuck board down first!
Whilst in the plate was still in the 4 jaw, running as true as I could get it, I centre drilled the end of the spigot, in case it might be useful to pick up on it for some other use at a later date.
I marked the PCD for the three chuck mounting holes using a sharp tool in the cross-slide (dimensions from the catalogue)
With heart in mouth, I removed the plate with spigot from the 4 jaw and tried it on the rotary table - it sat down beautifully, rock solid, with no lateral movement and absolutely flat - could not get a feeler gauge under it anywhere.
I marked out the three bolt hole positions on the scribed pcd line using spring bow compasses (dividing a circle into six by setting the compasses to the PCD radius and marking every other point when stepping round the marked circle )
I drilled the holes M8 clearance and counterbored them from the spigot side to take the M8 bolt head.
Here I made a big mistake, I thought (ha ha) there was enough meat in the plate to take what was a large counter bore (13mm) - wrong. On two of the counterbores, the drill burst through the edge of the rim - not by much, but really annoying. I had "step drilled" the plate up to 13mm, but on the final drilling, the drill grabbed on a harder patch of material at that point, the column of the mill I was using for the drilling shuddered and the drill bit split the edge of the plate. (I have in mind to make a column buttress support plate to replace the big spring washer - thanks to that thread elsewhere on MM http://madmodder.net/index.php?PHPSESSID=b7226c3f123aaf2323fc8bb973256494&topic=1226.0)
It dawned on me I should have turned down the bolt heads a bit first if space was too thin. I never thought of that until I had done it. I was really disappointed at being so stupid - but decided to carry on.
Here's the chuck mounted at last to the plate.
To fix the transfer plate to the table - using Circlip's patent back of envelope system - I made two "T studs" from 12mm steel bar.
The waisted section will allow the studs to ride up in the table T slots, the longer, upper diameter being turned down to 10mm.
The plate is drilled through 10mm and polished with a micro sanding drum in my Proxxon mini drill for a close sliding fit for the upper part of the stud.
The "clever" bit is to cross drill the plate in line with the 10mm holes and tap up to them M6, with a bit of an M6 clearance counterbore .
Two M6 socket head grubscrews have their ends tapered to cone shape for about 5mm.
The 10mm portion of each of the studs was marked with blue (felt tip pen) and inserted in the plate. The coned head grubscrew screwed in to mark against the stud.
Each stud was then cross drilled 4mm dia. at a position 1.5mm BELOW the mark left by the end of the cone.
Put the studs back, screw in the grubscrews, and the coned taper engages in part of the cross drilled hole and pulls the stud up as it enters into the hole, until the 12mm bottom dia. of the stud sits hard up against the upper part of the table T slot. The transfer table is thus locked down onto the table surface, being centred by the locating spigot.
I mounted the lathe face plate in the same way.
Here you can see where the 13mm drill burst its way to freedom - still makes me angry I didn't turn the bolt heads down.
To be honest, the lathe face plate is going to be of more use on the rotary table under my X2 mill, as the 100mm lathe chuck, even mounted on the rotary table with this "low profile" adapter plate, sits quite high, and headroom below the drill chuck is minimal. It will be possible to use finger collets/milling cutters with it, provided the work doesn't sit up too high in the chuck.
Maybe when funds permit, I can buy a lower profile lathe chuck - or maybe one day, a bigger mill!!.
I am pleased I got this project to work, and very pleased I could turn a register and make a spigot with some degree of accuracy.
Still kicking myself about not thinking of turning down those M8 socket heads.
I suspect the "coned" screw method of mounting is known by experienced engineers, but I had never come across it before - especially on the back of an envelope (literally) held up to a web camera on Skype transmitted from Bradford.
