Bed Grind-Harrison Lathe

[Madpiper]

Hi,
I have an older Harrison L5 that had the gap bed section missing. I was able to source a replacement gap. Is there anyone in Calgary (or Alberta) that can do a re-grind, provided the gap fits somewhat close?
Thanks

 

[combustable herbage]

HI maybe connect with @RobinHood he might have some info on that as I know he has a similar situation with one of his lathes..

 

[Mcgyver]

Perfect application for scraping. It is very difficult to grind V way geometry to be exactly the same so it mates existing geometry. The usual process to make a lathe, at least back when the fit mattered lol...... was to grind the bed then scrape the components to fit the bed. Also why when redoing a lathe that after regrinding a bed, everything is scraped to mate with it.

It would not be difficult to scrape it to perfection, as good or better than grinding, however, if not yet set up there's a bit of leaning curve and tools to collect.

 

[Chipper5783]

Hi,
I have an older Harrison L5 that had the gap bed section missing. I was able to source a replacement gap. Is there anyone in Calgary (or Alberta) that can do a re-grind, provided the gap fits somewhat close?
Thanks

Have you measured it? Put some straight edges along (even just a quality scale). Is it way off? Is it sitting high (have to remove material)? Maybe it just needs to be shimmed up? Where are you in Alberta?

 

[Lucky7]

First questions I’d ask is hardened bed or soft? Are there dowels/taper pins to hold gap piece in place accurately? Is the gap high compared with bed? To me these (and budget/time available) would answer question of grind vs scrape. Or just move on to another lathe. Even if the answer is grind I’d want to scrape the bottom of gap and mating surface of bed to good match before grinding.

 

[RobinHood]

Yes, the gap piece on my CMT URSUS 250 is missing. The gap is 10” wide. I am in the process (very, very slow process) of making a new one.

I plan on “building it up from parts” kind of like a LEGO set. The base and side walls will probably be of welded construction (base scraped after manufacture to fit bed).
The way surfaces will be machined and surface ground separately. If I get the geometry right, I might not have to scrape them - if not, I will. Then I will come up with a way to mechanically combine the base with the way pieces. I am thinking keyed & or pinned with bolts to hold it all together.

Max Grant (Swan Valley Machine Shop), is devising some fixture to mount a grinding wheel on so that he can regrind the ways on one of his lathes. If it works out for him, I might go down that route.

The URSUS has a massively wide saddle and even without the gap piece in, there is little overhang into the gap when using any chuck. I want the gap piece for faceplate and collet work (where the saddle is much closer to the HS).

 

[Madpiper]

Perfect application for scraping. It is very difficult to grind V way geometry to be exactly the same so it mates existing geometry. The usual process to make a lathe, at least back when the fit mattered lol...... was to grind the bed then scrape the components to fit the bed. Also why when redoing a lathe that after regrinding a bed, everything is scraped to mate with it.

It would not be difficult to scrape it to perfection, as good or better than grinding, however, if not yet set up there's a bit of leaning curve and tools to collect.

I did pick up a hand scraper for the project; another tool, another skill to learn.

 

[Madpiper]

First questions I’d ask is hardened bed or soft? Are there dowels/taper pins to hold gap piece in place accurately? Is the gap high compared with bed? To me these (and budget/time available) would answer question of grind vs scrape. Or just move on to another lathe. Even if the answer is grind I’d want to scrape the bottom of gap and mating surface of bed to good match before grinding.

I believe the ways are soft. The gap & bed do have a dowel system which should help alignment.
There are some chips to the edge of the bed ways, closest to the headstock (where the gap bed would have been fitted). How can these chips be built up; Ideally, id like a perfectly smooth transition from bed to gap piece.

 

[Mcgyver]

I believe the ways are soft. The gap & bed do have a dowel system which should help alignment.
There are some chips to the edge of the bed ways, closest to the headstock (where the gap bed would have been fitted). How can these chips be built up; Ideally, id like a perfectly smooth transition from bed to gap piece.

My first thought is I wouldn't worry about it, what's the win in filling it? .... and there's a downside ..... you're changing the geometry. Whatever you put in there could be tricky to get back in to the same plane as the mating way surfaces.

 

[Susquatch]

How can these chips be built up; Ideally, id like a perfectly smooth transition from bed to gap piece.

I'm with @Mcgyver on this. I wouldn't even try to fill them in. It would probably only make things worse.

However, even though the bed is cast iron and therefore difficult to deform, any damage done might have created high spots at the mating surface or on the main ways caused by whatever caused the chips. These have to be removed.

 

[Madpiper]

I’m somewhat new to machining; but my overall approach has been to learn what best practices, or gold standards are for a process or repair-and then work back to what provides an acceptable outcome I can achieve, and what I can live with. Lots to learn!

 

[Lucky7]

My first bigger lathe was a worn out 15” Colchester Dominion, over thirty years ago. Fixed many issues with that lathe and ran it for years, but never fixed the soft bed dings and scores. A regrind could have eliminated many but not all, but wiser old guys said why bother- it’s still an old worn Colchester. Would have had to build up the saddle with turcite and rescrape it… etc etc. Learned much from running that lathe, including what I wanted to see in its replacement.