Help Please: Top-Slide Angle Setting.

I've turned plenty of tapers and chamfers over the years but never previously needed better than the protractor scale on the lathe itself. Until now.

Lathe: Myford ML7.

Problem: Setting the top-slide for an external Morse taper, for the body of a spindle depth-stop to use on that lathe.

Reason for making this? The commercially-made depth-stop not accommodating work much longer than the chuck jaw depth.

Attempted: A long MT 2-3 adaptor-sleeve held by its parallel portion in an ER collet. A DTI in a QCTP block, plunger as near centre-height as I could manage, run along the sleeve's taper for each iteration of altering the slide-angle.

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Only.... No matter what I did to the angle, the DTI deflection range barely changed.

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Eventuality: Gave up on the indicator! Used the Tool-post block's blank sides as a sort of gauge of the top-slide's relative rotation against the sleeve.

Result 1): The taper far too wide.

Reset: A shim feeler-gauge between tool tip and sleeve, to try for equal gap at each end of the taper.

Result 2). Obvious, really. Well, the depth-stop body "fits" the spindle but only by line-contact. It does not transmit any rotation; and the draw-bar doubles as the stop itself; the threaded body acting as support and depth location. With no taper friction though, the device can slacken, losing its setting. This happened when I was finish-boring it, in situ.

It might enable its immediate task - three dozen rods of interchangeably-equal lengths - but I am Not Happy with it.

The only comfort is that if it moves in use, it will err on the side of safety.

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I tried what I thought the correct procedure (with the DTI), but either it can't be or I have missed something.

I'd be very grateful to know what, please!

I got my initial morse taper 1 angle by using trigonometry

fixed number of turns of leadscrew (so a fixed distance) moved dti point touching topslide body by the required distance as the topslide body moved past it

The DTI must be at 90 degrees on the horizontal plane

Took a while to tap the topslide to just the right angle, it was slightly finger tight for stability

Then cut a morse and tested it

Then scribed a line following the body of the topslide onto the cross slide with a sharp knife to make it a permanent alignment fixture when needed

When I make new ones I measure the diameter of the workpiece, about 10mm is the mouth of MT1 if memory serves

The first one you do is a total faff but if you scribe the topslide the rest are pretty easy

Edited By Ady1 on 29/05/2023 02:09:21

Youtube video of Joe Pie setting the top slide angle.

**LINK**

I use a original ground Morse taper sleeve which I set up true between centers or in the chuck running true. I then mount a finger dial indicator on center height. I run this along the Morse taper sleeve till I get no movement with the clamp bolts slightly loose. I then tighten the bolts and check taper again. Adjust till you get a zero reading. The dial indicator MUST be on center height.

As David says "The dial indicator MUST be on center height." He means the contact point of the indicator's arm but you probably understand that but so must the point of the tool cutting the taper. They need to at a matched height even if slightly higher or lower than ideal.

Martin C

Is it just a guide to stop a rod flapping about? - use a cheap 2mt collet pushed into the nose..

Nigel's original post:- Not sure why this did not work.

Attempted: A long MT 2-3 adaptor-sleeve held by its parallel portion in an ER collet. A DTI in a QCTP block, plunger as near centre-height as I could manage, run along the sleeve's taper for each iteration of altering the slide-angle.

Only.... No matter what I did to the angle, the DTI deflection range barely changed.

How long is the parallel portion? It would need to be getting on for the length of the collet to guarantee that the piece being held is not twisted very slightly off-axis. And is it guaranteed to be accurately aligned with the tapers anyway? In the taper adaptor's normal role, I'm not sure that accuracy is needed there.

Personally, I would use a 2MT centre between a centre-drilled hole in a short stub held in a chuck/collet/whatever and a tailstock centre (assuming that the tailstock is accurately aligned). I'm pretty sure that that is how I did it, last time I machined a 2MT taper - I think I had a centre to use as a gauge like this with a centre hole in the "blunt" end.

One of the fun things about model engineering - techniques can differ so much depending on what we have available!

If the sides of the top slide have been machined square, hows about a Chinese digital angle finder, claiming degrees to 2 decimal places. You could put it between the side of the cross slide and the front face of the chuck.

This turns a tricky accuracy problem in to a shopping opportunity.

I have been amazed by the accuracy of the cheap digital protractor. Tiny little thing, I zero it on the milling machine bed, turn it upside down and stick it on the bottom of the bed, 179.9 degrees

Robin

You could try using a DTI with an elephant foot tip.

Something is wrong there. Can you duplicate/mock up the set-up you used and post a pic? We may be able to then offer some advice.

Do avoid disappearing down the rabbit hole of the myth that tool or DTI centre height is critical. GH Thomas exploded that myth in his book Model Engineers Workshop Manual (p139). He did the math and concluded that having your tool (or DTI) ten thou above or below centre on a taper would result in an error of about one millionth of an inch of concavity over the length of an MT2 taper, and an error in the diameter of one end vs the other of some 0.00000135".

And setting your tool or DTI within ten thou of centre height is well achievable by the usual methods such as steel rule pinched between job and tool, or eyeballing the DTI pointer vis a vis the tailstock centre etc. Even with a tool or DTI height set 30 thou off centre height, the errors are still only half a thou end for end and 1.2 millionths of an inch hollow.

I think old GHT may possibly have had way too much spare time. (As do those who quote him on t'interwebs, I suppose!)

Thank you very much - some valuable pointers (!) there.

I've seen the various debates on the accuracy of tapers being affect by slight tool height errors, but had not appreciated how much this would affect the DTI as well.

Thinking about it, I recall somewhere advice that the probe also needs a disc-shaped face to minimise height error - though still needs its axis to be set as closely as possible.

Mine has the standard hemisphere, so presumably I saw the probe climbing over the curved surface by being off-axis, giving a wild error reading much greater than that of the top-slide angle error.

This shows I will need make a or buy a probe foot, and modify how the tool-post holds the indicator. As it is, it is evidently not lowering the axis of the probe sufficiently to be both horizontal and on centre-height.

I asked what I had missed, and it was clearly those two points!

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Diogenes -

The body is a guide for the rod, yes, but more than that.

It is held like a collet, with a draw-bar screwed into a short threaded portion of its inwards end, but the draw-bar's end face is the work-stop itself.

Both ends of the draw-bar are threaded for an appreciable length, so it can be screwed through the body for a distance appropriate to the work and the chuck. The protruding tail-end is then secured by locked nuts against a flanged support bush acting on the spindle end face.

The outer end of the body is bored out to a loose 1/2-inch to one-inch depth, and anyway its end face retreats into the spindle by about 0.1 inch. (Spindle bore, 0.60" )

The arrangement is to let work-pieces enter the spindle by about an inch. The bought depth-stop's minimum setting protrudes from the spindle by nearly an inch, the work-holding problem I am trying to solve.

The immediate project involves parts about three inches long, held in an ER collet for best concentricity. If I make a new body with a much longer tail-end spigot I could even extend the working range, sensibly by up to perhaps another inch.

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Nealeb -

The adaptor I used is so long it is hard to see it being very useful as that, at least not on a bench-drill! I think it is actually an extender rather than taper-size adaptor; but the parallel part is about as long as its taper part.

Also, the constricted space meant I could not hold its outer end on a tailstock centre, at least not without that at full stretch so compromising the accuracy anyway.

As to the tailstock centre-height's accuracy... well, yes, I should examine that. This is an old machine, after all.

So I'll try your approach, but will also see if it's feasible to re-fit the top-slide turned end-for end so it does not fight with the tailstock. Though I'd need ensure it also misses the headstock and keeps my hands well clear of the chuck or collet.

Edited By Nigel Graham 2 on 29/05/2023 11:43:42

See post above. About one millionth of an inch difference according to GH Thomas. I don;t think that is the source of your problem, unless you were a quarter of an inch below centre etc. .

A quick plug for GHT's gadget for making fine adjustments to the top slide; my photo shows the idea:

It might defeat the pirpose of the learning how to saet the Top sode, but the easy wayb out surely, would be to buy a 2MT blank arbor and modify that to act as the .l,ocation for the depth nstop.

It will have ground, and therefore better, (And probably be more accurate ) finish than can be obtained by turning.

Yes, a nice feeling of having achieved something, but will the end result be worth the effort, other than satisfaction?

Howard

I have had dial gauges stick so I thought all was spot on when it wasn't. Getting a dial gauge set horizontal on centre line often needs some inventive contortions and it is very easy to miss the fact that the back spindle is rammed against the dial dauge stand (Don't ask....).

Even after success with the dial gauge the taper is only rarely spot on in my experience. Mic blue and more tapping / faffing about until a decent blue smear is achieved.....

Once you have it right, run off a few for stock.

Martin

I did indeed consider modifying an existing tool, and even put aside for it something from my come-in-handy stock, that appears to be some special tool modified from perhaps a boring-head shank or slitting-saw arbor.

In the event I found a way to complete the immediate task, ending 34 aluminium rods to length; but I still want the depth-stop, and all the above advice has led to me considering my intended design more carefully.

It led too, to examining my two Baty dial test indicators more carefully, to find they both have two probe tips, one hemispherical, the other only slightly convex. I found ARC Euro sell tip sets to fit indicators with standard 4-40 UNF threads: I had not known of that standard. Happily, very careful measuring revealed the two Baty ones are so made.

In extremis a 6BA male thread would probably fit the socket - the diameter and pitches are very close, and the main difference is in the thread angle.

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After I finished facing the 34-off rods to length and drilling their ends for tapping, I looked at the lathe to gain some idea how to mount the DTI on centre-height. The best way seems an angle-plate that would temporarily replace the QCTP, to put the indicator's fixing lug below the top-slide surface.

So this is one enquiry that went further that I had thought it would!

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A note on that batch work.

I knew from the outset that drilling the rod ends to depth on the lathe would be very slow, laborious and tedious; and physically awkward and uncomfortable with a conventional tailstock.

So I broke the work into sections thus:

Lathe:

1) Face one end of each sawn blank.

2) Set a depth-stop on the lathe, and face all the second ends.

3) Spot-drill all ends, but drill one to about half-depth (so about 1/2" ).

Bench-drill:

4) Put a 3-jaw chuck on a Myford-accessory nose-piece fitted to a base-plate - I made this a couple of years ago, complete with table-register, to use on the jig-borer. Mount this assembly on the bench-drill, using the drilled rod for alignment, and standard T-slot clamps on the base-plate .

5) Drill all 68 ends to depth, taking advantage of the Meddings machine's speed, sensitive quill and comfortable operating access.

6) Lightly countersink all.

They are now ready for tapping, using a tapping-head on the Progress 2G bench-drill on its low speed. I have already set a Record drill-vice for this but the 3-jaw chuck will be better.

An aluminium-foil pie dish with a central hole makes a reasonable shield to stop most of the chips from falling down the chuck.

Edited By Nigel Graham 2 on 29/05/2023 23:50:12

I use just use a plain 'straight' bar (the type that used to come with Mercer / Verdict / Starrett etc) that clamps into the tool slot - it's about 1/2" X 1/4" and 2 1/2" long, with the usual type of cross-drilled sleeve for the indicator spigot at the business end.

I use quite a sensitive lever indicator, a tenths one, because a couple of thou error in smaller MT's will let you know that it isn't quite good enough when you come to fit them, and it doesn't seem to be much harder work to find a null-point with one of these than it is with a coarser one.

I set the centre height of the stylus ball by eye against the point of a tool-height gauge which seems to work well enough.

The backstop I use in the GH600 uses a fabricated brass 'cap' that screws onto the small amount of thread at the back end of the spindle, through which the screwed rod is threaded, with a 'top-hat' collar to lock it off.

The nose insert is a loose 'guide' that fits in the spindle nose to stop the rod flapping about.

I'm not saying it's the best-ever design, just offering it as food for thought..

I like your depth-stop design. It would not work in quite the same way on my Myford ML7 and Harrison L5 because those have no protruding threads or other locations on their spindle ends. A version would suit the EW lathe though, as its spindle pinion is retained by a collar held by a grub-screw acting on a flat on the spindle.

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The top-slide surface on the ML7 is too high to mount a DTI on it directly, so if I want that horizontal and on centre-height I need make some sort of bracket to hold them.

I think the rod set with the magnetic stand is too large and clumsy to use there easily. It also seems to use odd diameters too, as making additional parts for it is very difficult. Almost a case for replacing them completely, but I've too many things to do with too few round-tuits, as it is!

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Right, time to turn to Ketan's web-site and order that DTI probe set (ARC Euro).

i had this problem. your first attempt is on the right track, i my case as the DTI is not turning on the centre line of the top slide i was getting confused adjusting the angle correctly.