Thread: Workholding while making a large chuck backplate

I have to make a new backplate for a 10" TOS 4-jaw scroll chuck i recently got for my Macson, Im having trouble working out how to make it economically from plate. It needs to go on my A-Mount spindle which has a very short locating taper. Ill lay out the problems i need to solve below.

1: Material, I have some 1" mild steel plate that i can get it out of, but ideally i would like to make it out of something more resilient, is 4140PH overkill? should i be leaving it soft to save my already pretty beat spindle taper? What is commonly available in decent plate stock finished thickness is 7/8".

2: Roughing the blank out, I could theoretically treppan a disc out but i would be pretty scared when the 4+ kg disc came free at speed, i dont own an oxy torch, nor big angle grinder about the only way i can think of is on the rotary table on the mill but thats a bit hefty for my bridgeport and i dont look forward to cranking that handle 50,000 revolutions, any ideas? I imagine its just going to be cheapest to get it waterjet.

3: Order of operations, im thinking:

• first punch the 3" hole in the center and face it.
• flip the part over and while holding it with the outer lip of inside jaws in the center bore face the other side and rough turn the OD (Im very doubtful i can get a good enough hold)
• then hold it by the od with external jaws and form the stubby spindle taper (a hard job all on its own, still not sure how to measure such a short taper, is only about 7/16" deep)
• take it to the mill put the hole pattern in for the holding bolts.
• slap in on the spindle and finish turn it.
• profit?

Im open to any ideas on how to do it simply. Ill post some pictures and a sketch tonight.

Also if anyone has some 10" by 3" wall thickness steel pipe im all ears. haha

Regards - Ralph

I'd use cast iron by choice. Otherwise A36 mild steel plate would work but more likely to bruise if bumped.

As for cutting it, Aldi are about to have cheap angle grinders for sale - Saturday week I think. You can do it that way or you can pay somewhere to do it for you. Your choice.

Can't advise on work holding because you haven't said what you have that fits on the lathe spindle ATM. Lots of ways to skin that cat.

PDW

I have a 14" four jaw and 12" three jaw currently plus driving plate, centers etc, im primarily doing this to have a chuck with removable soft jaws and less mass, Are there that many ways to hold a big heavy disc by the id and turn the od? Thanks for the tip about A36 ill look into that asap. Im not really keen to use cast iron simply because of the filth.

I did something similar just the other day - I had a 10" square bit of plate around 25mm thick. I started by using a slitting saw to lop off corners to give me a 12 sided polygon. I clamped to the table and used an arbor in the horizontal spindle but clamping to an angle plate and using a vertical spindle would work almost as well. I then set the plate up on blocks and ran my large boring head around to smooth out the edges.
P1040205.JPG
In your case I think I'd get to the polygon stage and then mount it on the spindle to trim the edge. From memory with 12 sides there was only 6 to 8mm on the corners to clean up. I tried on the R/T but it vibrated too much and I couldn't mount it on the lathe as I only had a 40mm centre hole (reclaimed plate from an injection moulding die) and didn't want to enlarge it. The step in the photo was the results of the R/T experiment

There are a couple of ways that you could get the internal taper. I'd use a boring head to get the base hole done and then add the taper. Possibly the simplest is to mount the plate on your rotary table (concentrically) and then tilt the head of your mill over the required angle. A test bar, a dial indicator and some trig will help you get the angle right. Then it would be just a matter of doing a 360 degree rotation with the cutter in the hole and that should mill the angle into the hole.
Another option if you can hold it in the lathe is just to push the compound over to the right angle.
I also have a Tree boring head which would probably be fiddly to set up for a fine angle like that but is self feeding and so would bore the taper angle if you had a Z feed.

Pity it's 12 kg as otherwise you could send it over

Michael

I think that if you use a .0001" indicator you should be able to dial your top slide in accurate enough, but to get the diameter right after you have dialed in your topslide to the right angle you need to make a plug gauge, use one of your other chucks to gauge the gauge and blue it as you go.
If you are worried about holding it in a 3" hole to turn the OD put a bit of wood against the plate/disc then a centre drilled piece of steel against the wood and hold it there with your centre.
If Healesville isn't to far?
I have an 80 amp plasma that should cut it, (at a snails pace) and a 16" chuck on my macson with a TTA and a 2" drill to start the hole.

cheers, shed

Ralph, I just had a look at a table of chuck sizes (Lathe Spindle Fittings Page 2) to see what you are up against and I can't pick the one you wish to make.
Can you clarify which size?

Michael

That would be because its not in there strangely its not an A mount i have the name wrong, someone set me straight in a previous thread its actually a lang mount it has four studs in the back that go through a big slotted captive disk.Lang Lathes thanks for the photo of that really creative setup.

Originally Posted by caskwarrior

That would be because its not in there strangely its not an A mount i have the name wrong, someone set me straight in a previous thread its actually a lang mount it has four studs in the back that go through a big slotted captive disk.

here -
//metalworkforums.com/f65/t1995...32#post1910232

I wrote a detailed reply which vanished and I can't be bothered re-typing it.

Basically, use the big 4 jaw. Bore/turn the ID, face it off, turn the OD that sticks out past the jaws. Flip over, grip on the ID, centre using the turned OD portion, finish turn the OD, face off. If you use a decent amount of force on the ID and don't get too aggressive on the OD turning while it's an interrupted cut it won't move at all.

Now you can bore the taper after re-setting to grip on the OD.

Given you need to do the final turning on the spindle in situ, the odd thousandth of an inch runout isn't going to matter.

I've done this a lot making 10" flanges 1" thick from A36 plate that got welded to 3" diameter bar - rudder stocks, drive adaptors for a 200HP diesel engine and the like.

PDW

Thanks PDW ill go with that setup partially turning the OD and then flipping. I appreciate the time you all put into this and will post the results.

Ralph

When doing the interrupted cut on the OD, go slow and use HSS unless you like breaking carbide inserts. I think I was running about 30 rpm, maybe less, until I had the OD cleaned up.

Also the easiest way to hold the blank on the 4 jaw while clamping it is to centre-punch it then bring up the tailstock with a centre in it and pick up the punch mark. You can then hold the blank with the TS centre while tightening the chuck jaws. Saves needing a 3rd hand and crunched fingers.

I usually run a 1/2" drill through as a pilot hole then a 2" drill (because that's the biggest I have) then swap to a big boring bar so I can take a decent cut - usually a minimum of 0.125" DOC, might go 0.2" DOC for a 1" thick plate. I've the HP, gearing & rigidity to take a 0.5" DOC but not the need/nerve. Your machine sounds like it has at least the same HP/rigidity as my Monarch.

PDW

I'm actually part way through doing a similar thing. Making a 8 inch / 200mm back plate, my biggest chuck is a 8 inch 4 jaw.
Got a inch thick piece of plate from the scrap yard, cut it to about 210 square in the horizontal bandsaw.
Used the mill to drill a hole in the center then boring head to bring it to size
Pressed a shaft / arbor into it
Used the banksaw to clip the corners off it so had 8 sized
Mounted in the lathe by the arbor and went about cleaning up the OD. Interrupted cut but play it by ear on what your lathe will do.

That is as far I have got so far as I'm waiting to get the chuck before doing the rest but the plan for the rest is
Bring the OD to final size and do a facing cut (at least enough to give a clean surface to register on the lathe jaws when mounting it later)
Press arbor back out
Mount in lathe gripping on the outside
Bring bore to final size & do facing cut
Flip it around, do facing cut and cut the register for the chuck to mount to

Not sure if that may help you with some idea's on how to do yours

Cheers
Wayne