ML7 toolpost - Turns Under Load

Guys,

Something else I want to try and address while I'm fettling the ML7:

Sometimes, the tool post block rotates under load, ie the tool pushes it round. It's particularly prevelant when parting off.

The other thing is that there's no accurate way of ensuring the block/parting tool is at 90 degrees to the work; there are no detents or alignment features.

I stripped the topslide down just now, removed the threaded post, and flatted the upper mating face on the surface plate, same with the block. Re-assembled and it's no better.

Any ideas?

Look for a small locking pin in the bolting flange that should engage with a matching drilling on the underside of the top slide.

Brian

If you can cobble up a way of holding a facing tool on the compound perhaps by using packers and a clamp, remove the tool post and put it in your 4-jaw. Set the compound for about half a degree of dish and take a facing cut with the compound. This will make sure it's hollow bottomed. When you clamp it down it will be very firm. You could lap it gently on some fine emery paper to create an annulus for more friction but it shouldn't be necessary.

On my lathe, which isn't a Myford, I can set the toolpost to any angle and it will stay put under any load I put on it. Is it possible that the toolpost clamping handle is bottoming on the toolpost stud thread or the thread is bottoming in the handle if it is a blind hole. In either case your solution may be as simple as a washer.

Jim

You'll probably find the cause is that over the years the centre of topslide has deformed slightly with the tension of the nut giving a 'dome' on which the tool holder sits.

If so bolt the topslide to your mill table, lock the gib and using a small cutter say 6mm-1/4" touch on in the centre area around the bolt hole and take very fine skims off until the milled area is all over - personally I would not use a fly cutter - despite the appearance of overlapped machining marks the face will be much flatter than if the fly cutter isn't perfectly true.

Well that's what I did

Best - Ramon

Edited By Ramon Wilson on 10/11/2020 18:59:06

Not sure what sort of toolpost you have but the Dickson type is supposed to have a pin through it into the topslide to stop this. Essential if you want to be able to easily interchange tool holders and keep the same tool offsets.

The Myford size ones don't have the pin, its the T0 and larger that do.

You don't need the pin to interchange tool holders and keep the same offset, it's only if you rotate the post that the pin allows you to get back to the same angle.

Thanks all.

As I mentioned, I flatted both mating faces on the surface plate. I checked there was no discernable "rock" on either part (this is what I was wanting to eliminate).

The block requires a decent thickness of spacer above, and a washer of correct thickness to bring the hand lever to a position that clears the top of the quick-change toolholder adjusting screws when tight. I can't get a bigger diameter of spacer in due to it clashing with the locking cams.

Because of the spacer, the lock handle collar is way off the end of the threaded part of the spigot, so no issue there.

There must be some residual wavyness left on the topslide surfce, so I might try skimming it as per Ramon's suggestion. However I am wondering if it needs more surface area to grip at the top end.

Picking up on the third paragraph in the original question, I align the parting-tool holder hence top block of my ML7's rear tool-post by gently pushing it against the face of the chuck-jaws, using them rather like a vertical surface-plate, as I tighten the stud nut.

[Once I've found a spanner that fits.... I don't know what's happened, but the accessories I've bought for this lathe seem to use nuts of anything but a single, coherent series.]

I've used variants on this for the main tool-post, too; but sometimes find it convenient not to have a positive 90º location on that.

I have a Dickson toolholder - it's a hardened block with no pin. The bore through it though is quite a bit larger than the 7/16 stud in the top slide so can (could) float about a bit. The underneath of the block has a counterbore about 8mm deep and 20 mm or so diameter (that's an approximation as I write this ) I never had anything centring this toolholder to the stud. At some point I began to experience the sympton you have - realised that the top had distorted so carried out the op previously described and turned a spacer to fit the stud snugly with an easy fit in the recess. End of problem. I've had the lathe since new, about 40 some years now - elderly but still in good condition.

One short term easy 'get you by' if this moving of the toolpost occurs is to have a single layer of copy paper interspersed between topslide and the toolholder - the improvement to the gripping power at the same torque of the nut out of all proprtion to it's simplicity and a good trick to use for anything that needs clamping anywhere, mill or lathe and especially if the part is liable to distortion with tight clamping.

Regards - Ramon

Yellow pages are the way to go for me, rather than copy paper as I'm a stooge; well I spent many years living in Yorkshire.
Also having a copy is handy when you have clean work to do, say re-building a brake cylinder, or alternatively something you've just dismantled that's covered in grease.
Work on the book, closed like a notepad, and bin the page as soon as it gets dirty.

Bill

Have put all sorts of contraptions on my M topslide over the years and turning under load has never ever been an issue with anything except a goofy mill I made with an offset cam system for the T-nut

Maybe you need a bigger nut and washer, and it only needs to be hand tight, or the threads are worn at the tighten down loading point and flex under load when cutting

The main cutting force actually goes down the way when parting off, hence the broken tool issues experienced by many hobby users

My milling slide turned under load, but that's a common milling-on-the-lathe issue

g

Edited By Ady1 on 11/11/2020 00:39:25

Yes you're right Jason. I had to drill the hole (cobalt drill) because for CNC use very small shifts in the toolpost caused by parting-off were messing up the offset calibration.

I have a BXA tool post on my Boxford and take some hefty cuts with it. It does not have a locating pin or fixture. It has never slipped during a cut. In fact I cannot remember a tool post on any of my lathes ever slipping except by user error. Check that the compound T nut the TP is fixed with is below the surface of the T slot & not above or flush with it.

regards

Sorry guys I don't understand the points about T-nuts.

The threaded post fits into the topslide casting from underneath, is prevented from rotating by a pin, and prevented from dropping out by three grub screws. The threaded post isn't going anywhere. It's the thing that's fitted over the post - the quick-change block - that's turning.

Some lathes have a tee slot across the top of teh top slide hence the need for a tee nut on those. Yours just has a stud.

Due to the uneven balance of the topslide you may not have rubbed it flat on your surface plate, may be worth bluing it and than gently rorating the toolpost on it a few times then look for where there is contact. Even marker pen will do if you don't have the proper engineers blue.

I have a Bison clone of the Dickson type tool post, this has an anti-rotation pin facility where the compound slide has a mating hole drilled in to approx' 5 mm depth, certainly prevents rotation chances. I have also turned the tool holder 90* & drilled another matching hole directly opposite for the same effect if I have two tools set up .. rarely.

George.

edited typo's.

Edited By mechman48 on 11/11/2020 16:32:13

A thin aluminium ship between toolpost and slide is at least as effective as clean, thich paper /thin card and considerably more durable.

I tend to fit such automatically when refurbishing or resetting up toolposts.

Even effective against synthetic coolant. that stuff finds its way pretty much everywhere and makes just about anything slip.

Clive

The 3 grub screws in the Myford top slide are there to keep the 3 tapped holes clear of swarf. The 3 tapped holes are

there to attach the ratchet that is part of the Myford 4 way toolpost setup.

the 7/16" diameter post is press fitted into the casting from underneath and should not drop out. I agree that he pin is there to stop it rotating.

Rod

We may have tee nuts but our blocks also mount on a single stud and rarely swing. You don't need to be a gorilla to tighten them either.

Not sure how the grubscrews work, but are you sure the stud is not being jacked up as you tighten.

Just put the edge of a rule over the hole and check for daylight, it will show up a raised lip around the hole. If you have a big washer handy with a hole significantly large than the stud put that under the block and see if it works properly.