Lathe tool post mounting details

[WCraig]

Hi:

I wonder if someone with a PM 10X22 or 10X30 lathe could show me how the PM-supplied quick change tool post is mounted to the compound? My understanding is that the Precision Matthews lathes come with both an AXA QCTP and a 4-way tool post. I think PM modifies some parts to make the QCTP fit the lathe as they receive it from China. Does the 4-way still fit 'properly'?

The reason that I ask is that I have a very similar 10X22 lathe and I want to be able to use both an AXA QCTP and the 4-way. I've been puzzling a bit about the best way to do this. The key thing is that my compound has a boss (see arrow below) that sticks up. The 4-way has a corresponding recess and they fit together so that the 4-way is centered on the compound.

I think I need to mill the boss off flat and then make a new 'bolt' (part #11) to hold down the QCTP. I'm guessing that the PM lathes come that way from China and this is a modification they do? I can't bore a recess into the AXA tool post as doing so would remove the threads that hold the parts together!

BTW, the threaded stud with my AXA tool post (9/16", nominally 0.5625") is quite a bit larger than the 8mm bolt (approx 0.315") that came with the 4-way. Does Precision Matthews drill out the 4-way tool post with their lathes so that both use the larger fastener?

Thanks,

Craig

 

[Jim F]

Why use both ?

 

[WCraig]

I plan to mount the parting tool in the 4-way. There will be considerably less projection from the tool post and fewer mechanical connections so I hope it will be more rigid.

Might mount the knurler on the 4-way, as well.

Craig

 

[matthewsx]

QCTP will be plenty rigid on your machine, if you need more replace the compound with a solid plinth.

Yes you can probably use both, you have machine tools so any modifications needed are just good projects for building skills.

But the QCTP with a bunch of tool holders will do you good.

John

 

[WCraig]

In case anybody else stumbles across this, I'd thought I'd summarize what I did. The following are the relevant parts:

At the top is the compound as it comes from the factory (ie with the boss and 10mm hole). Below that is the new 9/16" mounting 'bolt' that I turned. I had previously disassembled the factory components and carefully measured the head of the supplied bolt. It was a light press fit in the compound and I think it was secured with some LockTite. After a bit of heat, the arbor press convinced it to come out. Note that there is a small index pin (just visible at the bottom of the old part) that prevents it from rotating when you tighten the tool post down..

To locate the existing hole, I used a short 10mm rod held in the drill chuck. BTW, I'd planned to do this drilling operation on the mill. But the 9/16" drill (shown above) is too big for the chucks I have on the mill which max out at 1/2". Only my drill press had a big enough chuck.

The actual drilling went easily--cast iron is so sweet! I had expected the hole to be a little oversize bit it was a very snug fit on my new bolt.

Now, I moved to the mill to remove the boss:

I did plunging cuts to remove the bulk of the boss. Only the final clean up cut was made using the rotary table. I didn't want to use a large diameter end mill to remove the boss all in one cut since such cutters have a little relief in the centre and might leave a slightly higher surface towards the centre.

All went well and a trial fit of the new parts is shown below:

Craig

 

[WCraig]

There was just one more step:

I used LockTite to secure the new bolt in place and then drill and tapped for a set screw to prevent it from turning or falling out. I used a fine thread set screw since the 'head' of the bolt is only about 0.150" thick and I wanted a few threads to engage. LockTite might have been enough by itself but I figured why not go all the way and provide a mechanical lock between the parts.

Here is the new quick change tool post in place:

Yes, I made the bolt a bit long and then forgot to cut it down before assembling everything with LockTite. I may still do that and modify the handle that came with the 4-way tool post to fit the new bolt.

Craig

 

[WCraig]

It came up on another forum that wedge and piston style QCTPs are different. Apparently the design/construction of piston-style toolposts leaves enough 'meat' in the base such that it could be bored out to fit over the boss on the compound. At least if the boss is cut down a bit. In turn, the remaining boss could be threaded for a stud (probably to be secured with Locktite). Net-net, I'm not sure if this would be easier or harder than the process I used. Probably about the same amount of work overall.

As noted above, my wedge-style QCTP has a threaded connection in the area that would otherwise have to be bored out. Perhaps I could have left a 1/8" boss but at that point there would not be enough threads engaged on a stud.

Craig