Scraping a bed ways longer than my surface plate

J

jcloucek

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Hey Gang,

I am thinking ahead about some time when I may want to scrape lathe bed ways. All the videos I've watched show I either need to have a surface plate or precision straight edge at least as long as the bed. I have to believe this is not the case. Watching luthiers, when they level guitar frets, their leveler isn't longer than the guitar neck. So long as they have enough resting on the leveled frets, their work carries forward. I suspect leveling and scraping a machine surface is like that, but I cannot find the right keywords/catch phrases to see examples and/or instructions on how to do that. I can't seem to find a chapter in the copy of Connelly I got from the library, for example. Can someone please point me in the right direction?

Thanks,

Joe
 
There are all kinds of ways to overcome obstacles. However, sometimes the increased effort is not worth the bother.

How long is the lathe bed you want to scrape?
 
Interesting project. Can you tell us more about the machine and your surface plate? Are the ways hardened? How bad is the wear? Measuring the problems before you start is useful and will give you an idea how much work will be involved.
 
It is all hypothetical at this point. Let's say it's my Logan with 50" ways, or my South Bend with 36" ways. My granite surface plate is 12x18. I do not own a precision straight edge yet. But let's say my budget only allows for, say, 18"- 24".
 
How would you scrape in a 24" straight edge with an 18" surface plate?
 
How indeed, ddickey! That seems like a technique not covered anywhere that I have seen. When you think of GIANT GIANT lathes and mills, you mean to tell me they have GIANT GIANT straight edges? That doesn't pass the straight face test. They may have a giant or even GIANT straight edge. There must be some technique of sliding a shorter instruments along longer machines that I am missing.
 
jcloucek said:
Hey Gang,

I am thinking ahead about some time when I may want to scrape lathe bed ways. All the videos I've watched show I either need to have a surface plate or precision straight edge at least as long as the bed. I have to believe this is not the case. Watching luthiers, when they level guitar frets, their leveler isn't longer than the guitar neck. So long as they have enough resting on the leveled frets, their work carries forward. I suspect leveling and scraping a machine surface is like that, but I cannot find the right keywords/catch phrases to see examples and/or instructions on how to do that. I can't seem to find a chapter in the copy of Connelly I got from the library, for example. Can someone please point me in the right direction?

Thanks,

Joe
Click to expand...
First comparing how an instrument neck is leveled and a lathe bed is the definition of apples and oranges. One you can use a ruler for a “straight edge” and the other need a surface plate and scraped in straight edge. Very few of the guys I see on YouTube I’d use as a reference for scraping.

Connelly refers to the use of properly sized straight edges many times the course of the description of scraping but it’s not a standalone chapter. I’d really suggest sitting down and reading the Connelly book as it’s as much about avoiding the pitfalls as it is about proper technique. And the pitfalls for me were assumptions that would have cost a bunch of time chasing my tail.
 
I could not say with certainty that large machines were not checked with even larger straightedge. I've seen 8-ft camel back straightedge stored in a shop with a whole family of others, all different lengths. 8 ft does not a planer make but you get the picture.

One of the kinks of rebuilding machines is that you've got to touch up your equipment, too. So even if the straightedge comes to you in perfect condition, you'll need to check it at some point.

In theory, you can scrape in a surface with any length straightedge. In practice, it seems impractical. I suspect that you could overcome the challenges with a lot of time and experience. It is reminiscent of building furniture out of pallet wood except maybe more so.

You might be much better off saving up your lunch money for the right straightedge, surface plate, etc. But if you consider the total cost, it might be cheaper to pay someone else or buy a fresh machine. Probably not what you want to hear. Maybe you could call it education? Or start on a smaller machine. Rebuilding machine tools is great fun but it inevitably results in buying more and more tools. If you are anxious to start something, rebuild the compound first.
 
The area under the head stock and under the extreme right (tail/foot stock) are likely factory and without much abuse. Optics and wires will work to cover the bed but a good straight edge is easier and less money.

jclouceck, I appreciate your question. I actually do. However, your life and good results from your project will benefit from following doubleoreo suggestions and saving for proper tools and edges.

Daryl
MN
 
I think the biggest obstacle you would have to overcome is determining if the plane you are scraping is correct. Without a straight edge to span the entire way, you could run out of material to scrape or be forced to remove a large amount by the time you have reached the end. Another chicken vs egg argument I suppose.
I would agree there must be a way to do it accurately as there are some pretty large old machines out there.
 
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