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taper turning on my "M" Drummond.

"Minnie" chimney casting machining

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frank bryan16/09/2010 10:00:17
3 forum posts
I need to turn the taper on the alloy casting chimney .Could I offset the tailstock to do this if so any suggestions please.
David Clark 116/09/2010 10:14:22
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3357 forum posts
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10 articles
Hi There
Two suggestions, if you have a boring head to fit the tailstock, turn a centre to fit the head and use it by offsetting the head.
 
My alternative.
Not tried this but can't see why it would not work, turn a centre in the 4-jaw chuck then offset that in the headstock.
Both methods are simple and save offsetting the tailstock and then realigning it.
regards David
 
 
 
ady16/09/2010 10:15:46
612 forum posts
50 photos
The tailstock has an offset facility.
 
Loosen the two bolts holding the upper to the lower section and use the square key next to the bed locking lever to move the upper section to the left or right.
Retighten when happy.
Reset everything when finished, and do it properly.
 
Or you can use the compound and leave the tailstock intact, but the compound can sometimes foul the tailstock, you have to set up the job then crank it through its full length to check it won't mess up half way through the job..
 
gl
frank bryan16/09/2010 20:45:29
3 forum posts
Thanks both for suggestions I will experiment and see how I get on.
John Olsen17/09/2010 00:36:50
1294 forum posts
108 photos
1 articles
Ah David, I don't think the one in the headstock is going to do quite what you want. I did use a setup like this for the columns on my Leak based compound engine. (ME 1983). The technique is used there to allow turning an offset foot and head on an angled column. hard to describe in words, and I don't have a photo handy, but  picture a turned column to go between a bedplate and a cylinder block. The back columns are cast and support the crosshead slides, but the two columnts on the front just brace that side. Now, to make things prettier, we decide to angle the columns outwards a little. So the middle of the column is easily turned between centres, but the ends now have to be angled to match the flat faces on the two castings.
 
So the ends are done by using an offset centre at the headstock end . The turning is then done at the tailstock end, the end face and a short parallel section that blends into the main part of the column. This is also done at the other end by turning the whole job around. As well as the offset centre, you need a drive dog setup that prevents any movement, eg wire the dog to the drive pin.
 
I can see this needs a photo, so I will pop down and take one this afternoon.
 
Usual ways of turning a taper are:
1/Offset the topslide...OK but limited length
2/Offset the tailstock...hard to set accurately for the taper you want, even harder to get back parallel again. (Taper will vary with job length so all blanks must be identical.)
/3 Offset centre in tailstock, eg boring head with a centre. Fine provided the boring head does not move in the taper, same proviso regarding blanks.
 4/ Many different sorts of taper turning attachments as made by lathe manufacturers and described by people like George Thomas . Probably the ideal way, if you happen to have one.
I guess CNC would be another way, but not likely to be relevant here.
The Unimat Sl also allowed angling the headstock
 
regards
John
John Olsen17/09/2010 05:00:51
1294 forum posts
108 photos
1 articles
A second thought:
Maybe what David had in mind was turning an offset centre using the four jaw chuck, then using that in the tailstock. (not the headstock!) That would give you a taper. The offset centre could be on a parallel shank to hold in the tailstock chuck, to avoid the need to make another taper, which would cause recursion. * There would be no way to fine tune the angle, but that should not matter for a chimney. You would know the length between centres on the chimney, you would work out the offset to give the desired angle, and then it should be close enough to suit anyone, although probably not close enough to use for making Morse tapers.
 
There are two things I will do almost anything to avoid, one is offsetting the tailstock and the other is tilting the head on my mill!
 
* Recursion...you need a taper to make a taper to make a taper.......
 
regards
John

Edited By John Olsen on 17/09/2010 05:04:59

Michael Cox 117/09/2010 10:01:34
555 forum posts
27 photos
It is not difficult to make a simple adjustable offset centre that can be fitted onto or into the tailstock barrel. I have done this on my minilathe and it is really simple to use and set up. The best part is you don't have to spend hours realigning the tailstock afterwards.
My device is shown here:
frank bryan17/09/2010 11:06:44
3 forum posts
Many thanks for the suggestions.I will try Mikes idea before disturbing the tailstock.Regards Frank.
David Clark 117/09/2010 11:34:36
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3357 forum posts
112 photos
10 articles
Hi There
I meant offset the 4-jaw chuck in the tailstock.
Turn the centre in the 4-jaw in the headstock, offset it and fit the 4-jaw to the tailstock.
 
Slip of the keyboard.
 
regards David
 
AndyB17/09/2010 20:53:46
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167 forum posts
7 photos
Good evening all.
 
Offsetting the tailstock is easy, as described above. It is just as easy to realign with an M type with the screw adjuster; count the turns when setting your offset, cut your taper, rewind the same number of turns back to centre. Check by turning a parallel between centres and measuring the widths at two points towards each end (to make sure that they are the same) or run along a known parallel with a DTI to make final adjustment.
 
It is a bit more fiddly with a B which is a loose fit to the base. (The ways are identical so B owners can swap for M tailstocks)
 
For those who don't wish to disturb their set up; use an indexable boring head in the tailstock with a live centre mounted. Set your offset and cut away.
 
If you have a taper to copy it is even easier; set your original between centres. Offset your boring head until a DTI runs true. Replace with part to cut and cut away.
 
Take shallow cuts and a moderate speed...yes I know, that is the proverbial length of a piece of string!!
 
Works for me every time, even on 1MT tapers!
 
Andy

Edited By Andy Belcher on 17/09/2010 20:57:39

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