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Boxford A gearbox rebuild advice

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Steve Veness27/02/2016 15:16:16
10 forum posts
5 photos

Hi,

I'm a newbie so apologies if this is all a bit basic or covered elsewhere. I should say I have posted this request on the Boxford Yahoo user group too, but no response there yet...

I have just become the proud owner a 1956 (? serial number DEH3656/A/5352) Boxford A. It's in need of a bit of TLC. Basically I am looking for some advice on strip-down and re-building the screwcutting gearbox.

After a few checks that everything moved freely I plucked up courage and started it up with nothing in the chuck. All seemed fine, initially forward, reverse, power feeds working ok screwcutting moved the apron at what seemed like a reasonable rate.

Then I tried changing the gearbox and with the lathe stopped) two things happened:

First the left lever jumped out of any of the 'top' positions (A, C or E). Then, more worryingly, the gear lever shaft (part no 303 I think) migrated to the left and dropped out of its righthand bearing - then everyting stopped. I switched off quickly, and was able to jiggle the gear level shaft back into place but when I checked to see if everything will rotate by hand it moves a few turns of the chuck in each direction before going no further (and I didnt want to force it). Switching the reverse lever to the neutral position allows the spindle to turn freely again but all is clearly not well in screwcutting-gearbox land.

I could probably guess intuitively how to dismantle the gearbox and reassemble but is there anything I should be vary of?

Nothing went seriously crunch so I am hoping any damage is very limited.

Thanks

Steve

Steve Veness28/02/2016 07:17:52
10 forum posts
5 photos

If anyone else needs to do this, this video link was posted on the Boxford Yahoo group. It's for another SOuth Bend clone but mechanically the same. Quite helpful for a novice like me. smiley

https://www.youtube.com/watch?v=w5CuDdhdess or google on "tubalcain logan lathe #130"

The guy doing the video has a nice style too

Martin 10028/02/2016 14:33:37
274 forum posts
6 photos

Sounds like lack of lubrication or gummed up old oil on the gears top right hand side in the boxford drawing, or on the gears on the levers. The shaft 303 is held in place by a taper pin visible on the gearbox outer casing boss

It's significantly easier to work on than a bike or car gearbox, worst bit is refitting to the assembly to the lathe bed when two pairs of hands make it so much easier

Boxford parts drawing

Photo here showing the taper pin location http://modelengineeringnorge.weebly.com/uploads/2/2/8/6/22864734/8407460_orig.jpg

Edited By Martin 100 on 28/02/2016 14:47:29

Bazyle28/02/2016 16:24:30
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6087 forum posts
221 photos

When you take it apart the awkward bit is the leadscrew cannot be taken off first so it is dangling off the end. Be ready to make sure it is fully supported to avoid bending it or cracking the casting. I suggest taking the saddle off the end first but wire up the end of the leadscrew inside of the saddle before final removal. This wire can suppor the screw as you release the gearbox and rest it on its front on the bench. then you can get at the nut to release the leadscrew.

As you take it apart can you have look out for a brass washer about 1/2 in hole. I've had one left over for 25 years not knowing if it is from the saddle of the gearbox. sad

Edited By Bazyle on 28/02/2016 16:26:14

Steve Veness28/02/2016 17:20:25
10 forum posts
5 photos

Thanks guys, got the gearbox off ok and found the cause of the problem... half the teeth missing on the middle 16t gear (partno 292) on the intermediate shaft. I say 16t gear but sadly it's now more like an 8t gear lol!. Could only find 3 of the broken teeth so I assume it's been a gradual process of destruction.

Looks like it's going to be a long and expensive process to fix. Hey ho - wish I'd bought a model B now and stuck to changewheels for screwcutting.

I can't see how to get the intermediat shaft out - does it just drive out from the headstock end? There's a central boss or bush on the intermediate shaft but it appears to be pinned with a blind pin rather than a removalble grub screw. (You can also see it in your photo Martin) . Any ideas?

Thanks

Steve

Ajohnw28/02/2016 17:56:08
3631 forum posts
160 photos

Can't help getting it out but if Boxford can't replace the gear try John Ward. His prices are usually surprisingly low really. I wonder how many old lathes he has saved. He will also make up T slotted cross slides for a far few.

**LINK**

John

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Steve Veness28/02/2016 18:14:05
10 forum posts
5 photos

ok thanks John... once the shaft's out I'll give him a call. Cheers

Martin 10028/02/2016 20:08:32
274 forum posts
6 photos
half the teeth missing on the middle 16t gear (partno 292) on the intermediate shaft.

I can't see how to get the intermediat shaft out - does it just drive out from the headstock end? There's a central boss or bush on the intermediate shaft but it appears to be pinned with a blind pin rather than a removalble grub screw. (You can also see it in your photo Martin) . Any ideas?

http://www.boxford-software.com/spares/3656GearBoxEng.html

£54 from Boxford not sure about VAT or postage

Sorry I can't recall the dismantle process, last time mine was touched was about 5 years ago but it was relatively straightforward. A good degrease and wipe might reveal taper pins or grub screws. There is nothing silly like left hand threads etc and nothing more required than spanners, pin punches and a copper/hide mallet

I seem to recall a taper pin on the leadscrew but outside the confines of the box, but I could be wrong


A QC box is way better than changewheels for altering feed rates!

Edited By Martin 100 on 28/02/2016 20:13:43

Robbo28/02/2016 21:28:08
1504 forum posts
142 photos

The intermediate shaft, as you say, is secured with a pin on that central "boss". This is a taper pin, you need to locate the narrow end by rotating the shaft and comparing the ends of the pin. Drive the pin out from the narrow end (meanwhile teaching Granny to suck eggs) for about 1/4", then rotate the shaft and pull it out from the wide end..

The shaft should drive out of the casing, but I think only out of the left hand end (the keyways are not the full length of the shaft so won't go out the other way).

Take care to keep all the gears in order and the keyways/dowel pin holes in line by judicious use of bits of wire. (Granny and eggs again!)

Steve Veness28/02/2016 22:13:12
10 forum posts
5 photos

Thanks Martin  and Robbo... all good advice, and things I might not have thought about tbh, so much appreciated.

It will have to be next weekend's job now as I'm off to the big smoke for another week selling my soul for fitlhy lucre (aka paying the mortgage) but it feels like I should be able to make good progress come Saturday!

Thanks

Steve

Edited By Steve Veness on 28/02/2016 22:14:38

Steve Veness06/03/2016 22:13:01
10 forum posts
5 photos

I have dismantled the gearbox and found the cause of my troubles. I have included a photograph of the middle 16t gear (pn 292) which is missing 7 teeth. I have emailed John Ward to see how much a new gear will be.

img_0617.jpg
The gear it meshes with looks ok apart from two teeth that appear to have their tops ground off - I have added a photo of that too. Any views on whether that one needs replacing too? I am hoping not.
img_0602.jpg
A couple of other photos too. The 80t tufnol idler has a tooth missing and an couple have gone - presumably where someone tried to change from forward to reverse while the spindle was turning. I am not sure how much of a problem that will cause - any views.
img_0603.jpg
And finally, the great at the changewheel end of the main spindle is also quite worn... I assume there's nothng to be done about that unless I source a new spindle ?? I am surprised it has worn as it meshes with a fibre reverse gear but amybe it had steel revers gears in the past
img_0559.jpg
Any comments or advice welcomed, thanks!
Steve
Michael Gilligan06/03/2016 22:47:39
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19324 forum posts
964 photos

Posted by Steve Veness on 06/03/2016 22:13:01:

And finally, the great at the changewheel end of the main spindle is also quite worn... I assume there's nothng to be done about that unless I source a new spindle ?? I am surprised it has worn as it meshes with a fibre reverse gear but amybe it had steel revers gears in the past
img_0559.jpg
Any comments or advice welcomed, thanks!
Steve

.

That's a rather sorry sight, Steve ... and it's the design weakness that I mentioned on this thread.

I have never seen one that badly damaged. That lathe has certainly not had an easy life crying 2

MichaelG.

Ajohnw06/03/2016 23:55:43
3631 forum posts
160 photos

I can't really tell from the photo but the gear on the end of the spindle looks ok to me. Not sure why but next to the tufnol gears the teeth always look shallow / less sharp. While Michael thinks it's a design fault and could be right having been on the yahoo boxford group for a long time now I've not noticed anyone having problems with it. Maybe because it's heat treated steel like the rest of the spindle. A better photo of the worse looking teeth would help. Hard to tell from an end on shot but I expect they are ok.

As strange as it may sound tufnol gears are known to outlast metal ones when in contact with them. They use the tufnol to quieten the train down.

The 80T looks like it has a tooth more or less missing. Best not use it as it is likely to damage another. That sort of thing can happen for all sorts of reasons. I wonder if some one has screw cut into a stop on the bed. I theory it can happen if the mesh is set way too tight. That may explain the broken teeth in the gearbox as well. The newer lathes of this shape have a different power feed arrangement and that can be run into a stop without any problems. It's easy to tell if the lathe has that. There will be a slot running along the leadscrew and a feed tension adjustment knob sticking out of the saddle.

I wouldn't be happy with the gear with a bit of the top missing but one way of telling if it's likely to be ok is to watch what happens as it meshes with one hand holding one side of the train and the other the other to provide some tension. You'll be able to feel if it meshes cleanly in that area or jumps etc.

I don't know if you have joined the yahoo boxford group but it may be worth while. Some one may have a spare 80T and unlikely but some one may have the other gear as well. There are also generally boxford and southbend gear on ebay. It can be worth asking one ebayer - theplaneironshop othewise known as

**LINK**

Many of the model engineer type used machine tool sellers may have them.

One thing for sure looking at the photo's all needs a really good clean and fresh oil before you use the gear train.

John Ward can be rather hard to get hold of. Visiting is one option if you are close the other is the phone now and again. Great bloke etc but he's often hard to get hold of and may not answer emails or reply to messages. He probably gets lots. Boxford will soon tell you if they have parts available.

John

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Michael Gilligan07/03/2016 07:29:47
avatar
19324 forum posts
964 photos
Posted by Ajohnw on 06/03/2016 23:55:43:

I can't really tell from the photo but the gear on the end of the spindle looks ok to me. Not sure why but next to the tufnol gears the teeth always look shallow / less sharp. While Michael thinks it's a design fault and could be right having been on the yahoo boxford group for a long time now I've not noticed anyone having problems with it. Maybe because it's heat treated steel like the rest of the spindle. A better photo of the worse looking teeth would help. Hard to tell from an end on shot but I expect they are ok.

.

Perhaps my over-active imagination then

I agree that a better photo [focussed on the teeth of the spindle] would help.

MichaelG.

Speedy Builder507/03/2016 08:45:23
2454 forum posts
196 photos

Hi Steve, I am a Boxford owner myself, having previously had a worn out Southbend. To me, there is a lot of work to be done - the lathe has had a very hard life. Before you spend too much, what are the bedways, saddle, leadscrew etc like, as to bring this lathe up to a reasonable standard, it may be cheaper to look for another one and then re-coup cost by selling this one. A bit pessimistic, but that is why I parted with the Southbend, but I was able to keep most of the attachments. Also, look at the bearings on the gearbox (or lack of). On my old Southbend, I had to get the toolroom to jig bore the old bearing holes and then make bronze bushes, replace the spindles and even get a new headstock spindle as the gear was so badly worn out. Having said all that, I have bought bits from J.Ward and was happy with his service.
Anyway, don't be put off by what I say, and good luck which ever wy you decide to go.
BobH

Ajohnw07/03/2016 10:00:39
3631 forum posts
160 photos

I had the same thoughts as you Bob and the more recent lathes with the separate power feed are a better option in some way. However a working gearbox may have a decent resale value but I'm not sure how much.

To me it looks like some one has used power feed and the saddle has run up against the head stock. The lathe may just have sat around for any length of tine once that happened. It would be worth looking at the lead screw to see if it's bent or has any other problems, engaging screw cutting and seeing how firmly and tightly that holds the saddle in position via the rack feed hand wheel. Rock solid is the answer to that with a little bit of for/back play some of which will be in the rack feed.

The difficult part for some one who isn't familiar with lathes is just how well it may turn. The best answer is to do some and see. The usual suspect in that area is the headstock bearings. Maybe for a start the OP could run the lathe at circa 500 rpm for 20min, stop it and then poke a finger in the back of the spindle and see if there is any heat under the rear bearing. Ideally that area should feel very warm. Almost hot in fact but if it does it may overheat with the lathe running at max speed.

John

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Martin Connelly07/03/2016 10:36:12
avatar
1938 forum posts
207 photos

John and Michael, if you look at the centre portion of the spindle gear where the tumbler engages there is clear evidence of wear in the photos as presented. The ends of the teeth in the one o'clock to 5 o'clock position look like they have been stripped off.

If a new spindle is out of the question but the general state of the rest of the machine is in good condition I would suggest it is a potential CNC conversion. A spindle index pickup and X and Z axis drive is all that is required to make a machine that can still be used for turning and screw cutting. The gear driven drive train is redundant when such a conversion is carried out.

If you think this is beyond what you want out of a lathe you should be aware that by using manual data input (MDI) you can drive a CNC lathe just like a manual lathe but without using the drive train or turning handles to move the cutter around the workpiece. If you want to go further into what is available in CNC you would have the basic setup required with that setup.

If you think you want to stay away from CNC then maybe you could sell it as a machine that someone else could convert to basic CNC turning.

Martin

Michael Gilligan07/03/2016 11:17:55
avatar
19324 forum posts
964 photos
Posted by Martin Connelly on 07/03/2016 10:36:12:

John and Michael, if you look at the centre portion of the spindle gear where the tumbler engages there is clear evidence of wear in the photos as presented. The ends of the teeth in the one o'clock to 5 o'clock position look like they have been stripped off.

.

Martin,

That's pretty much what I thought I saw ... but I deferred to John, because he clearly has more experience of Boxfords.

A detail photo should confirm the matter, one way or the other.

idea ... Your CNC [Electronic Leadscrew] suggestion is excellent

... Make a virtue out of necessity.

MichaelG.

Ajohnw07/03/2016 11:25:04
3631 forum posts
160 photos

That looks like it's down to the angle the photo is taken to me and if stripped off I would have thought the OP would have mentioned it. edit - the teeth don't go to the end of the spindle, they stop well short but not leaving enough to easily fasten an extension on.

Some people on the electronic leadscrew group have finished up driving the lathe with what is effectively a servo motor complete with a tacho to get accurate screw cutting. Must admit I have wondered but can see the possible problems with spindle speed variation.

Anyway really the bottom line is will it turn reasonably well or to an acceptable level. The gearbox isn't needed to look into that.

Mark is on here sometimes. He has been around them for even longer. He may have got the hump though as some one was rude to him. He does know his Boxfords so perhaps people can respect that.

John

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Edited By Ajohnw on 07/03/2016 11:33:32

Edited By Ajohnw on 07/03/2016 11:35:27

Martin Connelly07/03/2016 14:53:40
avatar
1938 forum posts
207 photos

Ajohnw, the reason the tufnol gears outlast the metal gears is that abrasive particles can become embedded in the softer tufnol and so abrade away the harder metal gears. This is a common happening when soft and hard materials are in contact with each other and there is relative movement. Shaping and polishing mirrors for telescopes can be done by putting the polishing compound on a pitch lap's surface and moving the glass over that surface. The glass is removed but the softer pitch is protected by the abrasive that embeds itself in its surface. As this lathe looks like it was never cared for the lack of cleanliness that is required for this mechanism to occur seems very likely.

Martin

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