On the vices and joys of machine tool reconditioning...

[NickG]

It's one of the things I'm sure my grandad could have told me something about but never got chance, I know he had some funny shaped "engineers scrapers" but I never questioned it any further. Cheers, Will have to do a bit of research, find it fascinating that people can make a large area of metal flat by hand!

[MuellerNick]

  I learned from some scraping hands

Yes, the best you can do, is get a beginner's course from say Forrest Addy. He does offer them in the USA. Look at PracticalMachinist, he offers classes there.
Don't take a class that lasts for a week, you will break down at day two. I even can't imagine how his pupils survive a 3 day class that lasts 8 hours a day. As a beginner, you can't scrape 8 hours. 4 hours and you are fed up!
Learn the basics, and you can build a lot on that continuing at home.
Or find someone who can show it to you. A few evenings with 2…3 hours will put you on the right track. The rest is "just" learning to understand what is happening, judging from the blue and the way you apply the blue. The time-consuming part in the learning curve is reading the blue and understanding its language.


And don't forget, metrology will be a hefty investment!


Nick

[steamer]

And don't forget, metrology will be a hefty investment!




Yes sir it is!......even a cheap precision level is not cheap!

and indicators

and squares

and possibly straight edges...

labor put into making masters....sometimes for one use!

ect

Dave

[ttrikalin]

What are you using for a master?.....and do you need to borrow any?

Ah, I have made a 45 degree prism which I have been scraping for a master. It is not ready yet. Although it carries spots over the whole surface, they are not uniform, and less than 20 per square inch. However, it passes the 3 papers test... 

For those who have not read about said test... it tests for straightness:

1. rest the to-be-tested master on the surface plate sandwitching three pieces of cigarette paper, one at each end, and one at the middle
2. draw each piece of paper sequentially as if to remove them-- If the master is straight, you should feel the same resistance

Connelly says (and I believe him, having done it sometimes) that this is more sensitive than you would think. It is rather easy to sense a difference in resistance.

Thanks, Dave for the offer, but for now let's see how my own master turns out... I will take pictures tomorrow night...

take care,
tom in MA

[ttrikalin]

And don't forget, metrology will be a hefty investment!

So true. I have lousy instruments...

1. a small chinese tombstone 9"x12", supposedly 0.000050" tolerance (over what distance? the ... certificate did not clarify)
2. another chinese tombstone 12"x18", 0.000100" tolerance (over over some distance)
3. an old Starrett Last Word indicator, 0.001" resolution 
4. a no name indicator, 0.0005" resolution
5. a Federal 0.0001" DTI, which was sticky and I restored (should post a story about the restoration thereof)

I do not plan to buy better surface plates... but I will buy a tenths indicator... I will fabricate hardware for indicator setups for measuring...

[steamer]

Have at it buddy!....

Dave

[steamer]

Hey Nick,

I just saw this vid of yours.....Damn man...I need to change my pants now!

<a href="https://www.youtube.com/watch?v=Y8NqeD73ZZ4" target="_blank">http://www.youtube.com/watch?v=Y8NqeD73ZZ4</a>

Dave

[Dave Sohlstrom]

Nick

I have a couple of mills made in China that were spotted the same as in your video. Took hours to correct them.

Dave

[ttrikalin]

OK, today I got 2 hours in the shop and decided to continue a tad on the lathe...  So I did six rounds on the lower bearing ways of the cross slide, and got to this



Marking is done with minimal dye on the tombstone...  and when its day you can "mark" without dye at all, by giving the ways a wipe with ethanol, let them dry, and the touch the part on the tombstone. I recall reading about this in Connelly... I was surprised to see that in daylight, it really works...

After the baby goes to bed I may have some time to check parallelism with the upper surface... It was within 0.0002" over the length of the ways last time in any direction, and I would not expect it to have worsened much if at all by now... 

Dave, Nick or others who know what they do... Some questions...

1. Connelly, I gather, wants me to attain 15-20 points per square inch, because these ways will be the template for the mating (upper side) ways on the saddle... I would say I may have gotten near the lower point (I do not show my 1 inch window in the photo... for reference, the narrow surface is a bit over half an inch...)

2. Would you say that the bearing is homogeneous? It appears that the points are not entirely evenly scattered, but this is a matter of opinion(*). I am tempted to call this bearing quality OK, but I fear this is optimistic.

tom


 (*) I could measure the distribution by digitizing locations of points and doing a Kolmogorov-Smirnov test against what I would get from a uniform distribution in each direction ... but let's see what you think first...

[ttrikalin]

And this is the lower surface of the swivel compound base, marked using the upper surface of the cross slide as a template:



As a reminder, the latter has been scraped enough to attain good marking:



1. In terms of bearing quality, I call the above two surfaces done.
2. I still have to check again for alignment... and because alignment and bearing quality are achieved at the same time, take point (1) above with a grain of salt.


The alignment tests have not been completed... especially for the whole assembly of cross slide, swivel base and swivel compound. Connelly gives a tolerance for the assembly of 0.0035" per 10" of travel. It seems to me that I can do much better, and I will try... but he knows what he's talking about and I may find this much more difficult than meets the eye. 

Still hanging in there,

tom

[steamer]

OK, today I got 2 hours in the shop and decided to continue a tad on the lathe...  So I did six rounds on the lower bearing ways of the cross slide, and got to this



Marking is done with minimal dye on the tombstone...  and when its day you can "mark" without dye at all, by giving the ways a wipe with ethanol, let them dry, and the touch the part on the tombstone. I recall reading about this in Connelly... I was surprised to see that in daylight, it really works...

After the baby goes to bed I may have some time to check parallelism with the upper surface... It was within 0.0002" over the length of the ways last time in any direction, and I would not expect it to have worsened much if at all by now... 

Dave, Nick or others who know what they do... Some questions...

1. Connelly, I gather, wants me to attain 15-20 points per square inch, because these ways will be the template for the mating (upper side) ways on the saddle... I would say I may have gotten near the lower point (I do not show my 1 inch window in the photo... for reference, the narrow surface is a bit over half an inch...)

2. Would you say that the bearing is homogeneous? It appears that the points are not entirely evenly scattered, but this is a matter of opinion(*). I am tempted to call this bearing quality OK, but I fear this is optimistic.

tom


 (*) I could measure the distribution by digitizing locations of points and doing a Kolmogorov-Smirnov test against what I would get from a uniform distribution in each direction ... but let's see what you think first...

First of all, stone that thing and mark it up again...I see some burrs...or spots so small they might as well be burrs

Look at the mark up again, and compare it to the photo....I suspect it will get better distribution.

I'd do like the following for a cycle and see what's going on.   If the pattern changes drastically, and I suspect it will, I would say your being too aggressive for the condition of the bearing.  Shorten your stroke and lighten your cut..




 It would appear your using a fairly small radius blade as the marking show very hard bearing.  You may want to use a blade with a bit larger radius

Cross your cuts at about a 30 degree angle...even on the bottom of the compound.....see the streaks in the blue on the top of the cross slide that you used for a master?....those streaks appear as little silver arcs...that is either dirt, chips, or burrs...make sure you stone the part before you mark it up...if it's dirt you will feel it instantly...it even sounds wrong during the mark up!

The best think to clean the part with?...the meaty palm of your hand....works very well...though you will have blue hands for a while....

I would leave the area marked "ignore for 1 cycle" ..just like it is....see if it hardens up...it's a bit low as you don't have bulls eye's in the middle of the marking....let them go for a cycle or two and see if they mark up with a bulls eye.

I would also to the area's marked "hard bearing" 1 cycle only....and see how the whole pattern changes...I suspect your touching on those area's only.....really

Your blue appears thin...but it's telling you where things are at.....leave that as it is a for a couple of cycles....just so we can see what's going on.

Dave

[steamer]

This is closer to what your after...not so much the number of points,..no I haven't counted.... but the points themselves....they are pretty much all the same size and evenly distributed.


That will give you the repeatability you desire.   and wear the longest.  The answer is to cut evenly...same pressure, and stroke length.

And you want bit better than 15-20 for a part your going to used as a master....I would anyway...but it takes a while.

Dave

[FLG]

Hi, I have been watching your scraping work, and Dave´s too in his SB9 rebuild tread, both are great and I been learning a lot, soon I hope to start scrapping myself on my chinese tombstone.

I have a question about the stone you guys use for clearing the burrs, I have seen this stone mentioned in some videos I have been watching, its a tin flat black stone...

This stone, its need to of some special kind? or grit?, here the only stone I could get is these ultra cheap 6x2" gray kitchen knife sharpening stone 

I'm following your work with enthusiasm!

Saludos

[MuellerNick]

Mostly agree with what Dave wrote.
Sharp eye re the burrs! 
personally, I don't want to see any blue spots that at the border of the surface. They bear a high risk of being overseen. And sometimes, they are incredibly hard to spot. So yes, stone them down.
A word about stoning:
Do not stone too much. You are scraping, not stoning. Just a few passes until you hear/feel that the burrs are gone.


Scraper radius:
This work looks small, so the radius of the tool gets smaller too. You ware working in small areas and everything scales down. 60 mm radius is what I would use here (and I use it most of the time for finishing).


Coverage/number of spots:
In the upper guide, the area in the left 1/3 looks good to me (with some spots left for improvement).
But I have to say, that the spots per square inch method is crap. Not the fact that you want to have a certain number of spots, but the fact that there is no repeatable way to measure them. Just make a thicker layer of blue, and the coverage shoots up. If the layer is thick enough, you have 100%
A better way is to observe how the spots develop. As long as they do get more, there is work left to be done. If they stay the same and you have to split them to increase their count, you can call it good.
The picture doesn't look like you are in the splitting phase, a few more passes to be done. Maybe you should be a bit more aggressive. My guess is, that you do work too cautious.


Hope that helps a bit.
Nick

[steamer]

Your probably right Nick...Most people scrape too cautious.    The radius seems too small to me at least on the piece....but I agree with your assessment that a 60mm radius is about right for the job.

I also agree with your comments about the stone....easy does it.

I suppose much depends on how heavy the blue really is....I'm sure Tom will show us shortly.   And as I don't usually use blue, perhaps I'm reading it differently so I defer to you on that.

 

Dave