Back in June 2009, I posted (under "How To") an idea for a very low profile transfer plate to enable a 10mm 3 jaw chuck from my Sieg C4 lathe to be mounted on a basic 100mm rotary table on my Mini Mill using "riser bolts" to engage in the T slots on the table.
Here's a pic. I posted in the thread of the finished item.
Recently I have up-graded from my old Mini Mill to a Sieg X3 Super, which gives considerably more headroom.
I had been given a 6" rotary table some time ago, but had never had the chance to try it on the Mini Mill, due to headroom restriction but now there was no reason not to think of a chuck/face plate adaptor for my bolt/spigot mounted lathe chucks/faceplate with the bigger (and truth be told, much more solid and accurate) rotary table. I also wanted to be able to mount my chucks/faceplate etc. directly to the milling table.
I started to think about what could be done with a 2" "slice" of cast iron, about 105mm dia. I had bought this as an off-cut from Mallard Metals in Birmingham (usual disclaimer). A simple "pocket" milled out of each side would allow it to be bolted to the mill table with strap clamps but would not allow it to be mounted to the rotary table.
The answer to achieve both seemed too simple - thanks to a chance conversation with a good friend, Ian.
(Now a big apology here if the following idea has been done before - but I cannot remember seeing this posted elsewhere. There have been some excellent threads/ posts on D1-4 and Myford adaptors, but nothing on 3 bolt/spigot mounted chucks such as found on the Mini Lathe/C4 etc. apart from the low profile plate as I made - see above)
After setting the off cut to run as true as possible in the 4 jaw, I faced it and turned the outside as far as the jaws to a clean finish. Reversed it in the 4 Jaw, clocked it to run true on the finished outside diameter, finished skimming the outside surface and faced the end.
I cut a register (shallow spigot) on that face to fit the back of my 3 jaw lathe chuck (72mm dia. by 3.5mm deep if memory serves) - like machining a chuck back plate.
At the same time, I marked off the PCD (86mm I think) for the three M8 bolt hole for mounting to the chuck and popped their position by dividing on the lathe spindle.
I mount my chucks and faceplate to the lathe using studs permanently set in the back face of each, protruding by about 15mm. I find it quicker and easier to use nuts/washers to fit these to the lathe mandrel, rather than fiddle around with M8 bolts/washers each time - just a preference.
With the cast iron still in the 4 jaw, I then cut a large, deep groove 9mm from the spigot end, 18mm deep and 16mm wide (a bit like an off-set cotton reel!).
It was then just a case of transferring it to the mill table, clamping on the groove with strap clamps and drilling the three chuck mounting holes from the spigot face into the groove, M8 clearance. so as to take the studs. The groove being big enough to accommodate nuts and washers on the ends of the chuck/faceplate studs.
Turn it over and re clamp on the mill table and mark the same PCD and drill two more M8 clearance holes set at 180 degrees.
These will take the ends of 40mm studs set in low profile (fairly "loose") T nuts set in the rotary table T slots.
To use this on the rotary table, clock the table up first on the mill bed and lock the bed.
Bolt the receiver to the rotary table - but only finger tight and clock up on the outside face of the receiver spigot, tapping it in the rotary table slots until it id also true to the mill spindle clock. Tighten the T slot nuts hard.
The chuck/faceplate can then be mounted and should be also true to the rotary table/milling head, assuming the register/spigot is accurately machined at the beginning.
A concentric indicator would be most useful in this application, but a simple DTI set up in the mill head should also work.
Here are some pics of the finished item posing on the mill table (not shown as fully bolted down on the table).
I would imagine other materials could be used, other than cast iron - but I happened by this off cut quite cheaply.
As I said earlier - this may not be an original idea (cotton reel mounting), but I have not seen it published before.
Its very simple and relatively quick to make.
The only real problem i had was in machining out the groove - I could not get my blade parting tool (the obvious tool of choice to cut the groove) as close as I needed to the work because the tool post overhang was fouling the jaws of the 4 jaw.
In the end, I ground down a cheapo brazed tip carbide tool with a square tip to take out the centre of the groove, following up with left and right turning tools. The dimensions of the groove are not critical - I made it to fit my studs/nuts set up.
I can also mount my 5" 4 jaw lathe chuck (plus its back plate) the same way on the rotary table, using the same adaptor - but head room is starting to diminish somewhat - even on the X3 mill!
I hope this idea may be of use to those with "Chinese" type spigot mounted lathe chucks (Sieg series etc.).
Peter
