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Cross Slide Scraping

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ybyo

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#1
Hello all,
I have 180x300 (7"x12") optimum brand chinese made lathe,
I was living hard moments while making heavy cuts and getting surface finish problem issues,
Especially when using cut-off tool the carriage assembly is bending sometimes, although top slide and saddle locked position,
So i knew that ways should be modified/tuned and since it's my first precision work i started from cross slide,
As you see from the photo, red circle marked positions was only contact area to surface plate. Actually i was waiting bad ways but not so this bad at all :) This surface was polished by the way but under what i thought, belt sander maybe?
Anyway, i started to hand scraping, tool is basically carbide bit brazed flat screwdriver, i used dremel sanding paper discs for roughing also. I did some deep scratches but generally result is better then i've expected.

Darker area is transferred blue from surface plate. How does it looked to experienced eyes, should i go on for few passes?
Low spots are under 0.01 mm (0.0005") from high spots (0.007mm avg)
I am working on carriage side right now using cross slide as master. It was bad either and got some good results so far.

Gib is also inspected and it is bended as you guess. I read about making gibs, few people advising to make from derlin, is it suitable?

Thanks
 

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Ulma Doctor

Infinitely Curious
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#2
Hi ybyo welcome to the forum,
from the picture, it looks like the ends are still low- you should continue scraping- concentrate in the middle of both sides until the ends get some blue
if you are not using a surface plate as a master, you'll be matching the cross slide to the carriage-
that geometry may or may not be correct and you may have a difficult time making things right, geometrically speaking.
if you scrape a concave or convex surface by using another concave or convex master, you'll pull your hair in frustration trying to make an accurate flat surface.
a better method would be to master the cross slide to the surface plate, then master the cross slide to the saddle
gibs can be polished, or scraped and bent straight again
delrin would not be my first choice of gibs, but for a light machine, it may prove satisfactory.
 
Last edited:

ybyo

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Jun 29, 2016
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#3
Ok then, i will continue working on cross slide a bit further, thanks for the advice,
Another issue is cross slide surfaces (bottom side with upper side) are not parallel to each other. This is effecting on top slide motion as well, is it worth to work on these area also? It is about 150 arcsec (0.07 mm over 100 mm).
 

Ulma Doctor

Infinitely Curious
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#4
i would first concentrate on making the bottom side of the cross slide first, getting that portion flat
then measure the top side for parallelism and scrape the top side from there
 

Sblack

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Jun 26, 2016
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#5
Since you have it apart, perhaps you should take the opportunity to put some oil grooves in they ways with channels to oil fittings on top of the cross slide. This will allow proper lubrication of the slide and make your scrape job last.
 

Dresden

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Feb 25, 2014
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#6
Your part is tipping or rocking on the plate, use a short knife edge straight edge on each side and start out with a double cut triangular file, check diagonally and across.
Twisted parts need more work as you may have two tapers in opposite directions.
 
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