ML7 toolpost - Turns Under Load

Jason's analysis of the possible reasons for the marks on the topslide encourage me to suggest that once the surface has been improved, it may be prudent to protect it from any further damage, there are only so many times one can mill a little off the surface before one is down to the canvas!

So, if using the Clog type clamp, use soft, or at least smooth, packing, under any tools and under the foot of the clamp. I don't see any problem using the quick change tool block, though as ever with clamping, it pays to clean off any swarf before tightening.

Rod

All,

The blue on the pin is from where I caught it with my finger, it's quite far up in the bore. I've removed the pins now anyway.

The feel of the block on the pin isn't tight, nor is it too sloppy, and as I said the pin is perpendicular. I don't think the fit there is an issue.

I'll try the block on the surface plate and report back.

See the bit I just added to previous post about checking that shiny ring around the base of the clamping stud. Looks like metal to metal contact there displacing the blue so could be sitting up on that.

Doc, it appears to me you have a good finished result there within the limits of your mill - I would trust the milled surface at this stage. I think you will find the block is hardened so unless you can find someone to surface grind it your only option would be to lap it to something of known flatness - not your new surface!

If you have something flat that you can lay a fresh sheet of wet and dry paper about 280 grit on, using plenty of paraffin and oil as a lubricant you may be able to get rid of those high spots to a degree of flatness acceptable.

Duncan has a point if your tool holder is a close fit on the tool post - if it's not square it would produce an uneven result. Before you do anything else try parting something off to see if it has improved the gripping power so far.

My toolholder is the same as Duncan's and has the recess in the bottom too - it was a very slack fit over the Myford post but like his did/does have a centering washer. I assumed that yours would be similar - I fitted a boss as said to centralise the tool post which also improved matters but

Perhaps a silly thought, but is it possible that the clamp handle is hitting the end of the stud?

An extra washer under the handle might clarify that, and allow full clamping load to be applied to the block.

If so, another job would be to make up a spacer to replace all the washers.

Howard.

Yes, using the fly cutter gave a much better visual finish, and I could very quickly finish it with metal polish to what I thought was an acceptable standard (in terms of both looks and function) on the surface plate. The faces of the square cover and the faces and sides of the valve chest were fly-cut, and they stuck together on their own after some very light polishing. Same with the cylinder valve face and the cover:








The face on the topslide casting I've just done looks terrible, but is in fact very smooth with no discernable (with a finger nail) ridges.

I did tram the mill such that the fly cutter took very consistent cuts over the entire arc, even at small depth of cuts like 1-2 thou. It also just removed some material - almost dust - as the back of the arc passed over the surface. So I was at the time happy that everything was OK.

I've always had issues with side milling - from day one. And this has never improved despite taking all precautions against chatter. The only remaining thing I've got left to try is to re-shim the column base using a much greater area of shims. I got it pretty much perfect, but had to use shims only on the corners, butting-up to the bolts (ie giving a triangular conatact area on each corner). I think this might be having an effect on vibration of the column. I've also go to down-rate the gas strut on the head to prevent it from 'floating' and I think being pulled into the work when drilling and vertical milling, but these are all things that have been covered before here in some detail, and I'm at the stage where I'm just going to do what I think is right as see what happens.

Thanks all.

This is with the underside of the block blued:





And with the surface plate blued:





These were with light hand pressure and slight turning.

It's obviously not consistent, so I seem to be wasting my time with trying to determine contact this way: sometimes it's perfect, other times it's not. It's only a thin layer of blue, so I'm assuming the perfect result suggests the block base is flat. If it wasn't I could never get the impression on the surface plate like that.

I did notice that the edges of the block around where the cut-outs for the toolholders are, haven't been finished. I might go around them with a file and chamfer everything, along with the hole surrounding the central pin, and all the rest of the holes in the block. Then a light rub on wet and dry and leave it at that. I'll give it a test, and if it still moves I'll use a shim.

Duncan may have spotted it.

My clone also has the top hat bush and I wonder if the block will clamp properly with the bush removed. Your photo with the spring shows the bush missing and a decent contact patch.

It may be that the inconsistent results, and the tendency to turn under load are both because of insufficient clamping force.

I would dispense with the spring (I thought that it was a pile of washers! ) and replace it by a solid spacer, long enough that the stud does not bottom out in the handle, so that the full clamping force can be applied to the block.

A spring may be suitable for ensuring that the block engages with a locating dowel, but will not apply enough force to hold the block on its own.

F = uR where the force is comprised of the coefficient of friction (u ) and the load applied (R ).

Obviously F is too little , you cannot change u much, so R has to be increased.

Get the block solidly held on the Top Slide, and it will not move, and the surface finish will improve. Rigidity is essential.

Howard

Edited By Howard Lewis on 14/11/2020 15:04:21

Sorry Dave you've lost me.

Photo with the spring shows the bush missing, but a good contact patch?

Mine doesn't have a bush, and if it gives a good contact patch without, where's the issue with not having one?

As I said, the block on the post is a reasonable fit. I wouldn't immediately think it would make any difference at all to the contact patch; it's got more slight play in it than anything like I can dectect in out-of-perpendicular of the post - it looks fine.

Get rid of the spring, or you will never fix the problem.

That spring cannot generate sufficient clamping force to lock the block, Even with the spring fully compressed, unless the ends have been ground flat, the force is likely to be off centre, so the result may be different each time.

My fourway toolpost can be set in any orientation, and clamped with the handle, (No spring ) and stays in place, even with heavy cuts.

I can see no reason why yours should be any different, if solidly clamped..

Just to satisfy my curiosity, turn up a spacer, to replace the spring, and tell us what happens!

Howard

Can I suggest that you place a piece of paper between the mating faces and try that before machining anything.

If the bottom face of the tool block were slightly concave that would help as well

Just a thought,is the thread in the nut square to the locking face of the nut? I once a had a 1960s two stroke engined English built scrambler,it was s/h when I raced it for the first time the centre nut of the clutch kept coming loose,despite someh ard work in the paddock, later found the thread in the nut was not square to the faces,Brand new nut immediatley solved the problem. Various toolposts on my Super 7 have moved but only when taking things to and above the accepted limit, Knurling with single knurls will move a tool post even on my Colchester,though of course a big long ring spanner helps solve the problem,Also intermittent cuts act like an impact driver and will rotate a small toolpost,

Way too late Roy!

Howard, the spring was there purely to allow me to apply a consistent downward load and still be able to turn the holder slightly (for marking the blue). Rather than applying simultaneous pressure by hand and turning the block, I thought I'd try and remove one variable by letting the spring apply the downward load.

I don't use it for clamping the block in use!

Thanks Nigel. I just checked that and its all good.

.

Clearly of no interest to anyone

MichaelG.

So I've flatted the sharp edges the best I can (I think it is indeed hardened), and chamfered the holes in teh casting.

Here's what I don't understand about this:

Block coated, clamped as per use (ie no spring!), to a tightness I can just turn the block a few degrees (pretty tight):





so contact predominantly around the post.

Then clean and repeat with the casting face coated:



Same result:



Clean, and double-check the first method by coating the block, and:



Completely different result.

Am I doing something stupid here?

Do I just go with the last result, because if it was severely out of flat, I'd never be able to get that result, and assume its somehow my technique for blueing that's at fault?

The stupid thing was that someone inserted the spring before you got the lathe. A spring that is so spindly could never produce a load sufficient to stop the block rotating on the damaged surface that you had.

Your last picture shows a much greater contact area.

If you clamp the block with a fair degree of force, you may well find that a ) the block no longer turns under load, and b ) the surface finish improves.

You now have a block which makes contact over a much larger area, showing that clamping force is what is needed.

If the hole in the block is much bigger than the 7/16 BSF Myford stud, make up a top hat bush to centralise the block around the stud. (IF you don't have one ) The thickness of the "rim" should be such that with your spacer in place, and clamped hard, the handle does not overhang the workpiece., i.e. is on the operator side of the Top Slide. (Just another of my hobby horses )

With the block tightly clamped, (You won't strip a 7/16 BSF thread with the forces that you can apply with just a hand )

Hopefully, two of your problems will be history. Please confirm, when you have time.

The spring can go into the "Come in handy one day" box to await a new career!

Howard

photos as promised.