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View Full Version : How would you repair this lathe topslide tapped hole?



LHC
01-30-2012, 07:56 AM
Hi folks -

I am slowly picking my recent lathe acquisition apart for cleaning, and discovered a quirk on the swivel portion of the top slide. There were two little shiny spots on the horizontal part of the slide near where the set screws go in to clamp the swivel.

Wiping off the oil, I discovered that the metal is actually slightly bulged up at the point where the screws enter the casting - and in one case there is a noticable bump on the surface that has been partially worn a bit.

Here's a picture of the topslide and the offending spots. You can see the top screw is actually some weird home-brew looking allen head screw with a trumpet shaped head. The flare has obviously been pushed into the casting too far and the top surface where it's so thin, has buckled up as a result.

http://i307.photobucket.com/albums/nn286/LHC_02/Raglan%20Lathe/P1020525a.jpg

Here's a shot of the side - it turns out someone must have re-bored and re-tapped these holes for 5/16-18 because I have learned from someone that has the same machine, the stock ones look to be 1/4-20.


http://i307.photobucket.com/albums/nn286/LHC_02/Raglan%20Lathe/P1020547a.jpg

Upon closer inspection of the spot that you can feel with your finger, there is what looks like a small breach of the surface from the tap, or a crack or something.

See here -
http://i307.photobucket.com/albums/nn286/LHC_02/Raglan%20Lathe/P1020552a.jpg

Now then, the bumps have to go. I am going to enlist a friend of mine to help me stone these down flat with the rest of the slide surface. However, in the case of the one with the little crack/breach/whatever, should a void appear in the top surface of the slide as a result, I am pondering how to repair this.

I have heard about metal filled epoxies that can be used to repair sliding surfaces but the name escapes me.

In any case, I'd appreciate any more ideas that people might have on this subject.

Thanks !

metalmagpie
01-30-2012, 08:13 AM
I have heard about metal filled epoxies that can be used to repair sliding surfaces but the name escapes me.

That would be Devcon. Buy a new can, stuff has a shelf life.

Davo J
01-30-2012, 08:16 AM
I would put thread inserts in the holes (helicoils) to reduce it back to the size it was.
After that I would place a nice flat piece of steel of the area and tap it down, then stone the rest off.
If you don't put thread inserts in, it will just happen again.

Dave
http://www.classicmotorcycles.org.uk/technical/technical_helicoil.htm

J Tiers
01-30-2012, 08:51 AM
I would recommend NOT USING A STONING PROCESS. It works, but wears down otehr areas somewhat, and may leave abrasive particles.

For taking down "bumps", use a "burr file".

This is a piece of old single-cut file that you rub on a sharpening stone or other flat abrasive to cut off the sharp points of the teeth. That leaves a flat-topped tooth with a sharp front edge. (rounding the edges of the piece is good)

After that, it will cut anything that sticks UP, but will just "glide" over a flat surface. I use them to remove burrs after a scraping pass. You know when you are done, since the file will begin to "glide" instead of "dragging" as it cuts.

Lest the more timid members should object to use of a "file" on "precision surfaces", the idea comes from the Connoley book on machine reconditioning.

Richard Wilson
01-30-2012, 10:43 AM
To be honest, I wouldn't worry too much about it. Yes you certainly need to get the high spot down, and I would just use the smallest finest file I'd got, there isn't much metal to come off.
What do do then? You could just replace the screws with Allen grub screws (no head) and carry on, or you could, if you have easy access to the facilities, helicoil it down to 1/4". I'm just wondering, with so little metal above it, whether the helicoil process itself is likely to do more harm than good. As a matter of interest, the www.lathes website has some excellent colour photos of the Raglan5", and if you look carefully, the hole for these screws seems to be pretty much right up to the surface of the slide.
If it was mine, I'd smooth down the surface, replace the screws with grub screws and leave it at that.

Richard

LHC
01-30-2012, 10:57 AM
To be honest, I wouldn't worry too much about it. Yes you certainly need to get the high spot down, and I would just use the smallest finest file I'd got, there isn't much metal to come off.
What do do then? You could just replace the screws with Allen grub screws (no head) and carry on, or you could, if you have easy access to the facilities, helicoil it down to 1/4". I'm just wondering, with so little metal above it, whether the helicoil process itself is likely to do more harm than good. As a matter of interest, the www.lathes website has some excellent colour photos of the Raglan5", and if you look carefully, the hole for these screws seems to be pretty much right up to the surface of the slide.
If it was mine, I'd smooth down the surface, replace the screws with grub screws and leave it at that.

Richard


Hi Richard -
That's what I am hoping to get away with. But I always like to think a step ahead and have a "plan b"...

I showed this to an acquaintance this morning who is a machinist - he works at the same place where I bought the lathe from. After laughing and proclaiming "that looks like something xxxx would have done" - some long gone employee of the place - he suggested the same.

I did think about helicoils as well but he pointed out there's no metal left to tap for the helicoil and it seems getting something to thread into 5/16-18 and get back to 1/4-20 is not going to be workable as the threads are just about crashing into each other. I had poked a 1/4-20 bolt in the hole and while it fits, it's tight up to the inner dia of the 5/16 threads.

He also pointed out the fact that there's precious little metal all the way along the top of the fastener - it's just the weird trumpet headed fastener that has caused the metal to bulge up at the entrance to the casting. He was surprised that it did not flake off already give the proudness of it on one side.

The end result is that I will stone/file it down with his assistance in a few days when he has a chance, use some 5/16-18 set (grub) screws and carry on if there's no big chunk that falls off the edge. If there is, then we will just make sure it's flat and hope that the fact that the void is on the edge, means there's an escape path for any swarf that might find its way in there at some point.

I'm just a newbie at all this stuff but it's quite entertaining with all the little puzzles that get presented as one takes an old machine apart...

Thanks for all the tips and comments.

Peter.
01-30-2012, 01:01 PM
It seems very odd to me that there should be wear marks on the top of the dovetail as well as either side. I should think it ought to be one or the other. Is it common to have this?

Mcgyver
01-30-2012, 01:55 PM
It seems very odd to me that there should be wear marks on the top of the dovetail as well as either side. I should think it ought to be one or the other. Is it common to have this?

No, it happens when the dovetail horizontals have worn to point where its bearing on the centre section. It's fixable, you mill some away from the centre and re scrape. Unfortunately these areas don't seem to get oiled properly and wear results

LHC
01-30-2012, 02:26 PM
No, it happens when the dovetail horizontals have worn to point where its bearing on the centre section. It's fixable, you mill some away from the centre and re scrape. Unfortunately these areas don't seem to get oiled properly and wear results

Maybe it's just my ignorance of the subject but I don't quite see what you are explaining here - can you explain it a little more ? Thanks

macona
01-30-2012, 02:41 PM
I would stone it, clean it, and forget it. It will be fine.

As long as you wipe it down after you stone it you will be fine. You won't leave anything to speak of. And if you did you would never notice and would get more grit in there the first time you cut a piece of cast material.

Mcgyver
01-30-2012, 05:01 PM
Maybe it's just my ignorance of the subject but I don't quite see what you are explaining here - can you explain it a little more ? Thanks

I hope I didn't misread Peter's Q....here's what i was getting at.

In the top pic, there are two yellow arrows roughly over top of the horizontal elements of the dovetail. These are the bearing surfaces (along with the two angled surfaces) of the dovetail. However if you look at the raised centre section between these two horizontal areas, there is a strip down either side maybe an inch or so wide. This may be caused by wear (or could just be staining or something, hard to tell from the pic). That;s what what I thought Peter had noticed, and my response was there if there is wear here its not not normal because the centre sections should not touch...if they do, its because the horizontal bearing surfaces have worn to the point where the center section is in contact. Clear and mud? :)

michigan doug
01-30-2012, 05:06 PM
The only really "perfect" way to restore that threaded hole is to pre-heat the whole casting, weld the hole shut, re-drill and retap, then rescrape it. And hope and pray it doesn't warp or crack in the process.

I wouldn't touch that with a ten foot pole.

What I would really do in real life is stone it flat and get on with it.

Finest regards,

doug

Mcgyver
01-30-2012, 05:16 PM
I wouldn't touch that with a ten foot pole.


+1

when i got my DSG that casting was cracked and had been welded. Didn't know until i got things apart. Welding had warped the part and had resulted in hard spots next to impossible to scrape. What a mess. Thankfully one the good folks had that very casting sitting around as extra...got it scraped it and the rest is history.

anyway, be extremely careful about welding cast iron machine tool parts especially involving bearing surfaces

Peter.
01-30-2012, 05:22 PM
I hope I didn't misread Peter's Q....here's what i was getting at.

In the top pic, there are two yellow arrows roughly over top of the horizontal elements of the dovetail. These are the bearing surfaces (along with the two angled surfaces) of the dovetail. However if you look at the raised centre section between these two horizontal areas, there is a strip down either side maybe an inch or so wide. This may be caused by wear (or could just be staining or something, hard to tell from the pic). That;s what what I thought Peter had noticed, and my response was there if there is wear here its not not normal because the centre sections should not touch...if they do, its because the horizontal bearing surfaces have worn to the point where the center section is in contact. Clear and mud? :)

Yes that's exactly what I meant. Seems pretty likely from the marks that the top has been rubbing.

LHC
01-30-2012, 06:28 PM
Yes that's exactly what I meant. Seems pretty likely from the marks that the top has been rubbing.

ok - after reading these comments I had to go to the workshop (it's become a cleaning room lately) and have a look.

I think they are stains - there was a lot of old "varnished" oil under the top slide and it does not look like wearing when I look at it now under the light.

And on that note - the little "breach" that I had shown in a picture above, I believe now is just a short scratch with a well defined start and end to it. Under the right light it becomes light in color and under another light with the right shadow, it looks dark like an opening in the material. I had to dig up a loupe and study it to find that out.

In any case, the comments on welding are only "preaching to the choir" at this end. From the little bit of welding that I have done and the reading I have done on welding cast iron, I won't be attempting that - or even trusting anyone around here with the skill to do it.

Thanks for all the feedback - this sure is a great learning experience.

duckman
01-30-2012, 06:37 PM
If it bothers you plug the holes and remove the bump, then set the slide up rotated about 15 and drill and tap 2 new holes the correct size. :D

LHC
01-30-2012, 06:57 PM
An earlier picture of the swivel slide before it came off the cross slide - you can see the buildup of goo and varnish on the right side of the top surface of the slide but not the left.
http://i307.photobucket.com/albums/nn286/LHC_02/Raglan%20Lathe/P1020465a.jpg

Here's the underside of the topslide itself.

http://i307.photobucket.com/albums/nn286/LHC_02/Raglan%20Lathe/P1020456a.jpg

Tony Ennis
01-30-2012, 11:31 PM
This is a piece of old single-cut file that you rub on a sharpening stone or other flat abrasive to cut off the sharp points of the teeth. ...

After that, it will cut anything that sticks UP, but will just "glide" over a flat surface...

That's worth the price of admission, thanks JT.

J Tiers
01-31-2012, 12:14 AM
Glad you like it... not my idea, but it works.

Rub it on the stone until every bit of every one of the teeth shows a reflective "flat".

burning chips
01-31-2012, 11:09 AM
Glad you like it... not my idea, but it works.

Rub it on the stone until every bit of every one of the teeth shows a reflective "flat".

Never a dull moment. Pun intended. I am going to get me a good file with smoth sides and start rubbing.

I really like this idea. Thanks from me for sharing your information.

strokersix
01-31-2012, 12:14 PM
Make a couple threaded plugs, screw them in with some adhesive, cut off flush, peen to hide.

Then make a couple new holes in the original size clocked a bit for virgin material. This assumes the original clocking is not critical.