Is my cross slide gib strip not ground properly?

stioc said:
I'm hopeful that if I sand down the back part of the gib strip the problem will be fixed. Not sure hand sanding will work or if there's a better way to do it. May be if I mount the strip on the mill using an angle plate or something and then running a drum sander disc across it. Or lay it flat on the table using mitee bites or something and then use an endmill/cutter to skim the surface.

But if I do need to make the dove tails parallel I'm guessing the easiest way for me would be to do it on my mill using a dove tail cutter. Question is what size/angle cutter will I need, is there a fairly standard size that's used by these smaller lathes?
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stioc, I will add to the list and pile on that the first thing to do with that lathe is to check the dovetails, on the cross slide and on the carriage, using dowel pins that fit approximately half way into the working surfaces. They need to measure parallel over their entire lengths. This also tests the gib at the same time, which needs to be put in place for the testing. The gib can be carefully straightened by pushing it measured distances and noting the results. A gib with spring in it is a problem unless the gap is tiny.

Edit: also make sure the gib is being held lengthwise, so it does not slide and jam the gap.
 
I think this is a somewhat common problem on the 9x20 and the reason i say that is so many folks have a failure of the crosslide housing and have to replace it or make a new one. Granted it is out of Zamak or some mystery metal. This is somewhat masked by the fact the crosslide handle is pretty small and there is no thrust bearing. Also if there is any slop it will chatter like crazy so you have to keep the gibs tight. But the fact it gets tight on one end and cannot be adjusted points to the dovetail being out of parallel. Mine was .002" tapered so I was able to scrape the two dovetails in. The compound was like .010 and I didn't have the experience with a dovetail cutter yet. So just replaced it. I don't use the compound as much as the crosslide and the little the compound is out doesn't effect chatter or finish but it's on the list. I'd suggest if you've not seen this vid go through both parts.
 
benmychree said:
Still, if the dovetail was not tapered, that would not cause binding.
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Understood. I'm just hoping I can get away with just removing the taper from the gib and not have to make the dovetails parallel because I'm not even sure how that's done or if it's possible.

benmychree said:
It would be a much better procedure to re scrape the gib side of the bridge to remove possible taper, also check the gib for flatness on the surface plate with Prussian blue or other marking medium for full bearing, it can then be used (after possible necessary scraping) to scrape in the dovetail.
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Can you elaborate on this. I'm trying to understand how to go about this as I've never done scraping (I like learning new things). To be clear, here's what I'm calling the various parts.

1. This is the cross slide aka the female dovetail
2. the gib or gib strip
3. This is carriage side aka the male dovetail

298100
 
Bob Korves said:
stioc, I will add to the list and pile on that the first thing to do with that lathe is to check the dovetails, on the cross slide and on the carriage, using dowel pins that fit approximately half way into the working surfaces. They need to measure parallel over their entire lengths. This also tests the gib at the same time, which needs to be put in place for the testing. The gib can be carefully straightened by pushing it measured distances and noting the results. A gib with spring in it is a problem unless the gap is tiny.

Edit: also make sure the gib is being held lengthwise, so it does not slide and jam the gap.
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Bob, re read the post, this is not a tapered gib that can be measured against, it is adjusted with set screws; the only thing that needs to be measured is the parallelism of the dovetails on the carriage bridge.
 
Thanks for all the replies gentlemen. I'm trying to absorb it all. @benmychree by checking for parallelism of the "carriage bridge" you mean the top flat part of the male dovetail (#3 in the pic above)? So put calipers across the bridge on the front part and then on the back part? Something like this?

298103
 
stioc said:
Thanks for all the replies gentlemen. I'm trying to absorb it all. @benmychree by checking for parallelism of the "carriage bridge" you mean the top flat part of the male dovetail (#3 in the pic above)? So put calipers across the bridge on the front part and then on the back part? Something like this?

View attachment 298103
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No, I mean as Bob Korves and others noted, take two dowel pins of a diameter that hits the dovetail angle about half way up and measure over to pins at both ends of the dovetail, and in between the ends to detect taper in the dovetails.
 
As others have stated the thickness of the gibb on this style doesn’t really matter. The sliding surface needs to be straight the variance will be taken up by the adjustment screws. Although it would help to be parrallel.
Looking at your picture of the gibb installed it really looks like the angle on the gibb doesn’t match the angle on the cross slide and the gibb is tilted to match??
The height of your screws could be a problem tilting the gibb.
Sanding the gibb or machining the gibb will most likely make it bow being so thin.
I e gone through the cross and compound on my 9x20 and almost done with my 14x40. Scraping all surfaces making them flat and correct. I’ve put oil grooves on flats and dovetails of all surfaces with oiling ports. Doing this made a 100% difference on the 9x20 and see it doing the same for the bigger lathe. Both compound and cross slide top had a slight bow. Suspect the cast wasn’t seasoned well and sprung when machined. Absolutely no hand fitting of pieces surfaces were machined and flaked to give the appearance of scraping but once put on a surface plate it told the story. Qi is not their strong point for sure. It’ll take some time and effort good luck on your journey.
 
The reason I say thickness matters in this case is because without the gib strip there's no friction (the slide is very loose of course) and even with the screws completely removed the gib strip sticks in one spot. This spot also happens to be the thicker part of the gib strip. So if I were to grind it down flat I think it'll resolve the issue of stickiness.

I just need a surface grinder...this is my scheme to shoe horn a surface grinder in the shop somewhere- even been shopping for one on craigslist for the past few hours but they take up a good bit of space which I really don't have much of https://orangecounty.craigslist.org/search/sss?query=surface+grinder&srchType=T

Besides, scraping is well beyond my knowledge and skills and I'll probably make a bigger mess of it :chemist:
 
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