Lapping ways or not?

[AndySomogyi]

I’ve got the knee scraped in, it’s perpendicular to the column in both directions by about 0.0002/8”. I’ve verified that the column ways are parallel to within a couple tenths. All the scraped surfaces make good contact and the knee slides up and down nicely.

But it’s a little tight at the very top 3-4” or so.

I’ve seen some people lapping ways, but I’m not really sure what to think about it.

Any thoughts here on lapping ways?

I’ve got some valve lapping compound, tried it on cast iron and does seem to cut pretty rapidly. But I’m a bit concerned about taking too much off and changing the alignment.

I don’t want to change the alignment on anything, maybe just a little up top so it slides a little easier?

 

[extropic]

Using that compound is a terrible idea. It will imbed in cast iron and continuously wear away the faying surface(s).

Timesaver brand lapping compounds are designed not to imbed. I don't have any personal experience with Timesaver so I can't comment (good or bad).

Timesaver Lapping Compound Yellow Label and Green Label Compounds, non imbedding lapping compound, manufactured by Micro Surface - Newman Tools

www.newmantools.com

I suggest there is something amiss with your metrology or else the parts would fit properly. If "it’s a little tight" you are close to completion.
Figure out what's off on your measurements and finish scraping it in.

 

[cathead]

I would leave well enough alone. From what I have seen, the tables wear out more quickly than knees anyhow.
Nice work on scraping to such accuracy. That takes a lot of time and patience and knowing what to do.

 

[AndySomogyi]

Using that compound is a terrible idea. It will imbed in cast iron and continuously wear away the faying surface(s).

Timesaver brand lapping compounds are designed not to imbed. I don't have any personal experience with Timesaver so I can't comment (good or bad).

Timesaver Lapping Compound Yellow Label and Green Label Compounds, non imbedding lapping compound, manufactured by Micro Surface - Newman Tools

www.newmantools.com

I suggest there is something amiss with your metrology or else the parts would fit properly. If "it’s a little tight" you are close to completion.
Figure out what's off on your measurements and finish scraping it in.

I’ve just read about the Timesaver compound, one of the issues I was concerned with lapping is it will charge the ways and cause wear, but the Timesaver is designed to break down.

I think I’ll just leave it alone. I didn’t scrape the column as it looked good and the dovetails were essentially parallel (within a few tenths, fatter at the top). I think there is a few tenths wear in the middle, and the knee normally never touches the top.

It was only a little snug when I adjusted the gib very tight in the middle of the column.

 

[vtcnc]

I think that is begging for trouble. The pursuit of perfection, in this case, is the enemy of good enough.


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[Richard King 2]

Where is it tight, the flats or dovetail? I thought you said you scraped the column in an earlier post?

Do you have a cast iron straight edge? Blue it up and set it on the top of the flats and only rub move it 1" not coming off the top. If it's the flat it will only blue up on the top edge and bottom end of the SE.

Once you figure that out and if it is only a few tenths you could scrape it, then knife smooth cut file and then a MS-24 Norton slip stone. It could be the dovetails too. But you won't know until you check the flats.

Remember you are going to oil it and I usually leave the gib knee loose .0003 tenths per side for a film of oil.

As the others have said I would never use lapping compound on it. If you did and wrote about it and I was Vtcnc I would delete it as that is terrible advice to give anyone.

 

[AndySomogyi]

I didn't scrape the column, it looked good, measured the parallelism of the dovetails with gauge pins and mike, and was about 0.001 wider at the very top, past the normal range of travel, but the rest checkout out decent, about 0.0005 fluctuation in width.

I have a 17" cast iron straight edge with a 45 degree bevel, I'll check the dovetails and flats.

I don't understand the mechanics of how the non-embedding abrasives work, so I can't comment either way.