PDA

View Full Version : dealing with raised gap due to lathe bed wear



isaac338
12-20-2013, 12:39 PM
I just got a Colchester Master 2500 lathe with a fair amount of bed wear. The issue is whoever was running this lathe for the majority of its life left the gap insert on the shelf, or so I believe. There's a couple thou ridge between the bed and the gap insert, enough to make the carriage make a clunk when it hits it.

I haven't yet removed the gap piece to make sure it's not just swarf caught underneath, but the carriage tightens up at the tailstock end of the bed so I'm pretty sure it's bed wear.

I know the real fix is to regrind the ways and carriage but that's not in the cards for some time, if ever.

Is there any way to smooth the transition between the gap insert and the bed? Maybe stoning a small bevel on the end of the insert? I realize with the wear the way it is it will never be an amazingly accurate machine; that's not a big issue, I just want it to not clunk!

Jaakko Fagerlund
12-20-2013, 05:12 PM
Install it properly and then have at it with an emery disc to smooth out the transition over a small distance like 5 mm or so. Doesn't affect anything else.

goodscrap
12-20-2013, 06:21 PM
how about taking a few thou off the base of the gap section, it could be milled with a careful set-up without the need for fine finishing that would be required on the ways, it would also be consistant with the remainder of the bed rather than proud after the transition and not raising the carriage when you pass over it.

if you mill too much off then it can still be shimmed with shim stock back to the right height if needed.

Brian

isaac338
12-20-2013, 09:14 PM
how about taking a few thou off the base of the gap section, it could be milled with a careful set-up without the need for fine finishing that would be required on the ways, it would also be consistant with the remainder of the bed rather than proud after the transition and not raising the carriage when you pass over it.

if you mill too much off then it can still be shimmed with shim stock back to the right height if needed.

Brian

I thought about that.. not sure I'm brave enough! Might be the only option, though.

I'm going to take it out and clean it religiously and see if it's still proud, I suppose.

isaac338
12-20-2013, 11:01 PM
Just gave it a thorough cleaning and no change - it's definitely due to wear. I think milling or grinding the bottom won't work as it's the inverted-V way that's worn; the flats at the top aren't the same size.

Anyone have any better ideas? Something about going at this thing with some emery makes me cringe.

jlevie
12-21-2013, 01:26 PM
I realize you said that you cleaned the seating surfaces, but check for dings and corrosion. Then consider scraping the mismatch out.

When installing a gap I was taught to oil the surfaces and then tap the gap section down with a large dead blow hammer while tightening the bolts to squeeze out the oil.

Jaakko Fagerlund
12-21-2013, 01:40 PM
I realize you said that you cleaned the seating surfaces, but check for dings and corrosion. Then consider scraping the mismatch out.

When installing a gap I was taught to oil the surfaces and then tap the gap section down with a large dead blow hammer while tightening the bolts to squeeze out the oil.
If the ways are worn, which usually is greatest at the chuck end, then scraping that gap provides non perfect fit, as the gap piece itself is not worn the same way. It comes closer by scraping, but it is hardly a job that I would do because the result is not optimal and scraping isn't exactly easy.

If you put oil between the two surfaces, it will not seat completely because some of the oil will be retained between the two surfaces, which means added thickness. It wll be minute, but would affect the results of scraping. There is no reason to apply oil there, as it is a non-moving component and was manufactured as dry fit.

jlevie
12-21-2013, 02:26 PM
Wear of the ways is going to occur on the most used area, usually near the headstock. In this case it occurred on the fixed ways but not on the gap section because the lathe was used (a lot) with the gap section removed. Scraping the only the gap section is something of a band aid fix. The ideal fix would be to install the gap and scrape everything back to true. But a band aid solution is better than doing nothing.

While you do have to know what you are doing and have the right test equipment scraping isn't all that difficult.

Davo J
12-21-2013, 06:47 PM
If it was me I would take a bit from the underside of the gap.
Whether you machine it off or scrape if off will depend on if you want to learn to scrap and buy the equipment to do it.

Dave