truing a lathe spindle in situ.

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truing a lathe spindle in situ.

This topic has 20 replies, 11 voices, and was last updated 6 June 2015 at 19:42 by frank brown.

Viewing 21 posts - 1 through 21 (of 21 total)

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4 June 2015 at 11:20 #23922
Gordon W
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@gordonw
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4 June 2015 at 11:20 #192338
Gordon W
Participant
@gordonw
I have a Chester 8" lathe. I want to make a better, more accurate, dividing attachment, using a gear wheel on a stud and expandable plug. The problem is the end of the arbor is not very accurate in the bore. The bore is nominally 20mm. Any ideas for improving it? Without stripping the machine, no one anywhere near with a lathe. Just the last 40mm or so at the change gear end needs doing.
4 June 2015 at 12:01 #192341
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Gordon W on 04/06/2015 11:20:52:

… Any ideas for improving it? Without stripping the machine, no one anywhere near with a lathe. Just the last 40mm or so at the change gear end needs doing.

.

Gordon,

I don't know the lathe, but … assuming that there is a 'banjo' or some similar attachment point available: You could make a bracket that supports a bushing with a machine reamer [or maybe a boring bar] sliding in it.

MichaelG.
4 June 2015 at 12:19 #192343
blowlamp
Participant
@blowlamp
Could you remove the Top-Slide assembly and mackle up some way of mounting it to the rear of the headstock to permit use of a boring tool?

Martin.
4 June 2015 at 12:21 #192344
Neil Wyatt
Moderator
@neilwyatt
Do you have a milling machine?

If it can be positioned correctly and both are sufficiently rigid you may be able to mount a boring tool on the mill table and take very light cuts.

Neil
4 June 2015 at 12:31 #192345
Gray62
Participant
@gray62
When I bored out the spindle on my GH1330, I used a line boring setup. Long boring bar mounted in a special toolpost holder, with a bearing in the spindle taper and a specially made bearing mount attached to the rear of the spindle. Using this arrangement allowed opening out the spindle to accept the ful 38mm diameter right through the spindle (it is slightly constricted in the middle in manufacture) As the rear bearing support is outside of the spindle at the rear, you can bore right through and true up the full length of the spindle, Just need to take care not to damage the taper in the front of the spindle.
4 June 2015 at 13:50 #192352
KWIL
Participant
@kwil
Does the outer surface of the spindle run true? If so you could machine a clamping ring to use that surface to centralise your gear.

Edited By KWIL on 04/06/2015 13:51:16
4 June 2015 at 13:52 #192354
Bowber
Participant
@bowber
Got any photos Graeme? I've been thinking about doing the same with my WM280.

You could true it up by hand, a lot of work but do-able.
Or make a hand operated tool that's located inside a sleeve screwed onto the thread on the end of the spindle.

Steve
4 June 2015 at 15:41 #192364
Gordon W
Participant
@gordonw
Thanks for all the quick answers. I did have an idea to make a long ,over 15" long, boring bar but decided it would not work. I think that making a mounting for the topslide at the gear end and a shorter boring bar seems the best way. Simple and cheap, and I will need a better indexing plunger so might double up. Heavy bit of angle would do and a few holes drilled in the headstock. Would like to clean up right thru' as the middle is tight on 20mm but ok for 3/4". Can probably do that by hand, but the steel is quite tough.
4 June 2015 at 22:20 #192411
Clive Foster
Participant
@clivefoster55965
How about mounting a 20 mm Rotabroach or similar cutter in a 20 mm bar and feeding via the carriage. If the bar is made a close running fit in the hole produced by the rotabroach the cutter ought to be sufficiently well guided to run true. May need the bar relieved in places to reduce surface area in contact with bore. Probably wise to make arrangements for lubrication and do job in several small bites, 1/2" maybe, withdrawing between cuts to clear chips etc. Obviously work with minimum bar extension. Especially when starting.

20 mm Roatabroach cutters can be got with reduced diameter mounting shanks for £15 to 20 (ish) so costs aren't completely unreasonable if the job works "just like that". I've used the shank guided cutter principle in the past, albeit with a boring bar style cutter not a rotabroach, which did the deed OK despite chip evacuation problems. I turned a wide groove in the bar behind the cutter to take the chips. Not enough chip space so lots of 1/8" or less peck feeds. D shape around the cutter would have been better as providing more space and also supporting the cutter against the back wall of the newly cut bore.

Clive.
4 June 2015 at 23:10 #192414
John Stevenson 1
Participant
@johnstevenson1
Really, really silly idea and well out the box.

However not knowing the lathe it way work with a bit of jury rigging.

How about turning the headstock round and setting up a tempory drive, thia way you can just bore as normal.

Probably have to pack it a bit as the vee in the headstock won't sit in the vee but all that means is to just higher the tool a tad.

Bricks, flames, second hand £5 notes, can take it all.

Edit if this works, forget the £5 donation and just send a new keyboard as this one can't spell for toast.

Edited By John Stevenson on 04/06/2015 23:12:03
5 June 2015 at 00:13 #192421
Bowber
Participant
@bowber
Posted by John Stevenson on 04/06/2015 23:10:15:

Really, really silly idea and well out the box.

However not knowing the lathe it way work with a bit of jury rigging.

How about turning the headstock round and setting up a tempory drive, thia way you can just bore as normal.

Probably have to pack it a bit as the vee in the headstock won't sit in the vee but all that means is to just higher the tool a tad.

Bricks, flames, second hand £5 notes, can take it all.

Edit if this works, forget the £5 donation and just send a new keyboard as this one can't spell for toast.

Edited By John Stevenson on 04/06/2015 23:12:03

Or pull the spindle out and reverse it in the headstock and turn, probebly easier than turning the whole headstock

Steve
5 June 2015 at 10:40 #192455
Lambton
Participant
@lambton
This is one of the problems of lathes being made down to a price in far away countries. To be fair to the makers not many customers would find the bore inaccuracy at the rear of the mandrel a problem.

I do not think you will be able to overcome this fault without taking the mandrel out of the machine and having it bored out accurately on a proper lathe like a Colchester or DSG!
5 June 2015 at 10:44 #192456
John Stevenson 1
Participant
@johnstevenson1
Posted by Lambton on 05/06/2015 10:40:36:

This is one of the problems of lathes being made down to a price in far away countries. To be fair to the makers not many customers would find the bore inaccuracy at the rear of the mandrel a problem.

I do not think you will be able to overcome this fault without taking the mandrel out of the machine and having it bored out accurately on a proper lathe like a Colchester or DSG!

.

AT LAST —- IN PRINT.

A Myford isn't a proper lathe
5 June 2015 at 11:10 #192460
blowlamp
Participant
@blowlamp
Posted by John Stevenson on 05/06/2015 10:44:11:

Posted by Lambton on 05/06/2015 10:40:36:

This is one of the problems of lathes being made down to a price in far away countries. To be fair to the makers not many customers would find the bore inaccuracy at the rear of the mandrel a problem.

I do not think you will be able to overcome this fault without taking the mandrel out of the machine and having it bored out accurately on a proper lathe like a Colchester or DSG!

.

AT LAST —- IN PRINT.

A Myford isn't a proper lathe

I was going to offer to help the original poster, but my best lathe is only a Harrison so I'm not taking the chance.

Martin.
5 June 2015 at 11:12 #192461
Gordon W
Participant
@gordonw
Well, well! I was awake half the night thinking about this. On further inspection the end bore seems more like bellmouthed than eccentric. I liked the idea of setting up the top-slide on a bracket, but can not see how to get it in a straight line. So am thinking to turn a plug with a slight taper and keep trying until it fits, then clock up and see how far out it is. Does not need to be dead on for what I want. It is a proper lathe made in the east with a bit more capacity than a blue thing. I could turn the spindle round but don't want to disturb it until I have to, the deep groove bearings have only been in for 8 years and are still good, touch wood. Can open up the middle with a burr on a stick I think. Thanks for the suggestions, they will come in handy one day.
5 June 2015 at 14:23 #192494
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Gordon W on 05/06/2015 11:12:33:

Well, well! I was awake half the night thinking about this. On further inspection the end bore seems more like bellmouthed than eccentric. I liked the idea of setting up the top-slide on a bracket, but can not see how to get it in a straight line.

.

Gordon,

Others may disagree, but I still think my suggestion of a guided Machine Reamer is the way to go. … A simple bracket with a big bush adjustably mounted on it. … Make the bush in the lathe, using the reamer and facing-off at the same 'chucking' [nothing else is critical on the bush].

You are only going 40mm deep, so there's plenty of space to let the reamed hole guide the reamer. Big tap-wrench and due care & attention if you do it under power.

MichaelG.
5 June 2015 at 18:53 #192534
Neil Wyatt
Moderator
@neilwyatt
He should have a mini-lathe , mine has a bore that is concentric to better than a thou at the tailstock end

(I know because many years ago Mike Chrisp questioned the wisdom of me using a collet to mount a dividing device in the bore, so I checked it.)

Another option – measure the eccentricity and make the collet to match, and always fit it with two matching marks.

A 2" gear or ring of holes that is 3-thou eccentric will have a maximum error of 0.17 degrees – enough to be unacceptable for some uses, but OK for others.

Neil
6 June 2015 at 16:08 #192605
Gordon W
Participant
@gordonw
I finally got round to doing some measurements. The bore as far I can tell using calipers and mike is bellmouthed about 5 thou at the end. Dial gauge shows about 5 thou' eccentric. So will make a slightly tapered plug, don't think the eccentricity will matter much. NB I don't have mill or any other machine tools, costs have to be kept down. This lathe is pretty good considering price etc. never had to adjust tailstock, mandrel 3 morse taper is spot on.
6 June 2015 at 18:11 #192616
Neil Wyatt
Moderator
@neilwyatt
Rough shape a bit of softwood then hammer it in, pull it out and you'll get a pretty accurate idea of the size and shape of the 'ole.

Neil
6 June 2015 at 19:42 #192625
frank brown
Participant
@frankbrown22225
As the outside of the shaft is "true", I would use this as the reference. So get hold of a big piece of steel, Bore a hole in it to be a good fit on the shaft. Drill and tap some holding grub screw positions. At the other end block up the end and drill for a 1/2" pilot bar. Build a boring bar with a 1/2" pilot and an adjustable tool length. Assemble so the tool bar is held in the tool holder on the saddle, but sits slightly behind the main spindle. Now assembling the guide will centralise the tool. So switch the lathe on, the work piece (shaft) is rotating, so pull the tool forward with the saddle to cut the hole.

On reflection, basically same method, but the "hole blocker" should be fastened to the tool bar and run in the shaft extension. Now you can back back the tool out of the guide to increase the "feed". ( tool offset).

Frank
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