Lathe unwanted taper

Part 2

You can use the bar between centres with a dial gauge on the saddle, whenever you have need to offset the tailstock in the future and want to return it to the correct alignment.

If you have a boring head consider making a centre to fit one of the holes in it, put the boring head in the tailstock and use the diameter screw of the boring head to offset the home made centre; that way tyou don't need to disturb the tailstock offset, and you have a nice screw adjustment to set the amount of taper you're turning.

Also, now you've made the test bar, set up a DTI on the bed/saddle running on the right hand collar. Slacken the tailstock bed clamp, and the barrel clamp slightly and wind out the tailstock barrel, pushing the tailstock casting itself off to the right hand end. If you observe the DTI whilst winding the handle, is should give you an idea if the tailstock barrel is projecting in line with the bed.

In some ways, the Myford setup is slightly easier as there are only 4 bolts, so there is less chance of "bending" the bed.
Also the mounting bolts are able to "push" as well as "pull" with respect to the lathe cabinet/workbench. 
There's a hollow bolt under the bed which runs in a threadded hole in the cabinet raising block.

Passing through the lathe foot is a thinner stud which goes though the afore mentioned hollow bolt and is retained in the cabinet.
This means that you can impart a true twist, without pulling the tailstock end of the bed downwards.

I hope this reads OK as I've not had time to proof read it as dinner's ready.

Good luck

Bill

p.s. there is an argument which suggests that the test bar should be a thick walled pipe, as it would deflect less under its own weight, but I can't imagine it would make much difference in the sizes of our "hobby" lathes, and also you would lose the advantage of being able to use it between centres to set the tailstock.

Edited By peak4 on 11/11/2017 23:03:04

Edited By peak4 on 11/11/2017 23:03:49

I suspect the change of alignment when the tailstock barrel is locked is down to the locking mechanism. A simple clamp on the barrel will inevitably move it slightly when tightened. Larger industrial lathes sometimes use two curved pads opposing each other so, in theory, the barrel doesn't move when clamped.

Andrew

If you skim the two collars at the same setting, but reversing the bar between the two skims) you can get them very close in size. I take the 0.0003" difference with a pinch of salt as I don't believe I can really measure to a tenth whatever my micrometer claims:

If you have a boring head ....

Simple little gems like that make rreading these posts worthwhile! Locked safely away until needed - unless I forget it!

.

Schlesinger describes such a bar, in some detail ... The bore is done in several stepped diameters [to approximate a taper]. But I agree it's probably only relevant to the acceptance testing of toolroom-class lathes.

MichaelG.

.

P.S. He does mention that "Deflections caused by the spring pressure of the dial-gauge plunger are negligible if this pressure is less than 3 1/2 ounces."

... Which I find quite reassuring.

Edited By Michael Gilligan on 11/11/2017 23:56:37

That's pretty much what I was describing Neil, but with a longer projection on the left hand end, so it can be held in a chuck for the initial setup of any required twist in the bed.
Unfortunately I lost mine due to a shed roof leakage and a subsequent attack of tinworm.

Since then I've found a 2 morse extension bar, but unlike most seen on the net these days, it is nicely ground all over. Ex military from Anchor Surplus in Nottingham years ago.
I now use this as a test bar from the headstock spindle taper, and for between centres use, add a blank stub arbour to the female end. Again not up to calibrated test bar standards, but adequate for my use.

I can get more "tenths" DTI deflection by gently leaning on the lathe than the bodged "test bar" idnicates.
Our lathes normally just ain't that rigid unless you are fortunate to have a high quality toolroom machine.

I originally thought I'd come up with something novel, then subsequently read that it's been a dodge for donkey's years.

For the home made centre in mine, I used an old broken solid carbide centre drill., fitted to a mild steel sleeve to take it up to 1/2" to fit the hole in the boring head.
Obviously not the easiest stuff to re-profile, but since no-one told be how I should do it, I came up with yet another bodge.

The Clarkson T&C Grinder was near the lathe, and I have a flexible drive shaft with a drill chuck on the end.
Another drill chuck on a spindle was secured to the bed of the Clarkson and the broken centre drill chucked up in it. Drive for the nescent centre was provided by the flexible polishing arbour, itself driven by the Myford behind me. Hardly conventional I assume, but did the job nicely. Yes I did cover the lathe bed with paper towels first.

Bill

Edited By peak4 on 12/11/2017 00:22:16

Thanks Bill for the detailed explanation, the Wm280 comes with 6 mounting bolts, 4 on the H/S side 2 on the T/S, will give it another go this morning...thinking about it, I used a 12mm "precision" steel bar which was fairly long, dont recall how much it extended out of the chuck, but must have been 500mm or so. Could it have slightly bowed under its weight?

I've not done any calculations but at only 12mm, I'd have thought it would sag a little bit, plus a bit more due to the pressure of the DTI tip.

With 4 mounting bolts on the headstock, I'd have thought it possible to fix it down pretty rigidly, such that the two at the tailstock end could drag that end down a bit with respect to the, now rigidly mounted, headstock.

Bit of a tangent - when I was a kid 10 or 11, Grandad asked me if I had a testube I didn't want. I gave him one to make a level - he knocked a hole in the end of the tube and fastened it to a long length of hose pipe. By filling the pipe at one end until water appeared in the test tube he could establish a level over a long distance.

Steve

A friend of mine recently bought the WM290 complete with makers cabinet.

A rigid cast iron plinth, it certainly isn't. I loaned him my big crowbars and precision level, along with some basic instructions of what needed achieving. He has his own DTI. We has a play for a couple of hours together and I retired back home. The following day he went out and bought something to bolt it to the concrete floor of the garage.

The base of each of the two pillars on the stand has 4 mounting holes, so with careful shimming and the level, plus 8 Rawlstud anchors in the concrete floor, he was able to get both pillars level and vertical. Thus the lathe itself then has a rigid mount at both ends, independent of each other and firmly fixed to the floor, to allow differential shimming of the lathe mounting holes if required.

It was remarkable how just adding a single thin shim to just one of the 8 mounting studs under the cabinet changed the readings on the DTI.

I think it took him the best part of a day to drill the floor for the 8 anchors and shim it all up to get the cabinet bang on level.

Bill

For folks who've never used a water level;

I've just had a new garage built over in Buxton and made one of these myself to check various levels as the building progressed. The builder himself hadn't seen one since his apprenticeship and the guys working for him hadn't come across one at all.

In my case I used a spare gallon plastic container with a brass fitting near the base to accept a long length of 5mm bore plastic pipe. This leads to a 2' length of 2x1" timber, with a spare steel rule attached. I then plugged the plastic pipe into a length of translucent CO2 line from a mig welder, clipped that to the steel ruler, and terminated the lot with an old motorbike petrol tap. ( I added another one at the container outlet.)

The container can then be stood at any convenient place in the garage at about the level you need to measure.

Note that the container stays put, and you wander round with the ruler and pipe marking the walls accordingly.

To make the fluid more visible, the commercial ones seem to add a bit of flourescein to the water.
Not having such stuff to hand I took the filling wadding out of a normal coloured highlighter pen and squeezed the ink into the water. Seems to work fine.

Don't forget to open both petrol cocks and the lid of the container. A friend of mine didn't quite think it through and used a borrowed one of these water levels to set the RSJ when he was building his garage. He used the container at one end and the tube at the other, leaving the cap on the bottle. the end result was a lean to one side of about a full course of bricks after he'd cast the two concrete padstones for the beam.

I got mine without the cabinet thinking it would be difficult to level without adjustable feet, so I built my own on leveling feet....still a hassle to line up tho!

Regarding the level, I filled it up with isopropanol and dyed it, the thinner the liquid the more responsive it gets and although it's homemade it's pretty sensitive, not pretending it to be a starrett, but I could read a 0.02mm shim with ease, good enough for me!

So yet again, this morning I had another go at leveling the lathe, as suggested I opted to start from scratch, so I loosened the lathe mount bolts all 6 of them, and proceeded with leveling the headstock and tailstock ends. There was so much adjustment  I could do via the bench adjustable feet as would have ended up with a seesaw, so I got as close as I could with the feet and the continued adjusting by tightening the 6 lathe bolts to the bench.

After a while I managed to get both HS and TS level, so I tried a test cut to see how close I was. I used the same test piece I had yesterday but reduced the overhang to about 4 inches. This time round there was no tool chatter, so proceeded with the test cut, result 0.1mm difference, wider part at the HS end 

Continued with test cuts and adjusting the level until I got identical readings on the test bar, that left me with a slight twist to the lathe bed, but I'm happy with it, I'll do a double check with rollies dad method

Leveled HS end before test cut

Leveled TS end before test cut

Final position of leveled HS end after test cut complete

Final position of TS end after test cuts complete

Edited By ChrisB on 12/11/2017 16:49:13

Edited By ChrisB on 12/11/2017 16:52:09

Quote:

If you have a boring head consider making a centre to fit one of the holes in it, put the boring head in the tailstock and use the diameter screw of the boring head to offset the home made centre; that way you don't need to disturb the tailstock offset, and you have a nice screw adjustment to set the amount of taper you're turning.

Exactly as described in my book 'Workholding for Machinists' - recently reviewed by a chap called Neil.

There is indeed, nothing new under the sun.

Regards, Tim