Scraping a bed ways longer than my surface plate

[durableoreo]

The cheapest way I can think of is using a sensitive level. Get the casting level based on the un-worn parts at either end of the ways, then use a level to measure tilt. If the level bears only at 2 points, you can scrape those areas down to level and use a much shorter reference surface to connect them. It will be a pain in the neck but a big project like this will always involve some trouble.

It would be nice to be able to cross check your work. At some point you will doubt everything and it's a real boost to the confidence if you can check another way.

There's a video of a guy doing some precision work using a bare camera sensor and a laser pointer. He set up the laser somewhere stable and moved the web cam along the rail. It was similar to an autocollumnator but cheaper and a lot more IT skills.

There's some other guy who cast a bunch of rails to fix up the bed of a lathe. It's taking so long that I lost track of what they're doing. I think that strategy would be the most expensive because you'll need a foundry and planer.

 

[Turnaround]

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 double oreo suggestions and saving for proper tools and edges.

Daryl
MN

As everything runs submersed in wet, gritty lapping compound, crankshaft grinding machinists say "wet grinders are made to wear themselves out." I have a older Storm Vulcan crankshaft grinder with a gang of wear on the bed where the tailstock lives when doing Chevy length cranks. With me using two chucks, the result of the tailstock wear is that the front and rear centerlines of the crankshaft point out into different directions, and are not on the same centerline as the bed of the crankshaft grinder or each other. With the defective centerline alignment, a spinning crankshaft bends around the front rod journal, and then that journal winds up being ground with a half of thousands taper sideways. The three rear journals grind to under a couple of tenths. I would like to place vertical standoffs along the whole length of the bed, and then find a laser beam/optic that would paint a mini spot on my bunch of vertical standoffs. That way, I could measure up from the worn bed surface up to the painted laser/optic spot, and then be able to calculate how much to scrape off the original, non worn portions of the bed. Have you every seen affordable optics that present a small enough dot image, that I could use such spot image to measure from the worn bed to the tiny spot/dots on all the bunch of vertical standoffs accurately?

And a second thought, I bought a Makita scraper that is in good shape. Does anyone offer a tool insert that would hold an inch or so shaped carbide scraping bit into my Makita scraper?

Turnaround out in Raeford, North Carolina

 

[ltlvt]

Keith Rucker did his Monarch and used an optical measuring system to check the bed. It was determined that it would best be to leave it alone and focus on the saddle. When a surface plate is recalibrated, they use the similar optical method to check flatness on the plate to be resurfaced. After you said it is all theoretical so forget the price of the optical device and just and imagine the method used to map out all the highs and lows.

 

[m1kemex]

Is there any way to efficiently and effectively and affordably scrape in a lathe without optics and longer straight edges?

How did they build the first straight edge when there were no straight edges?

I've had this idea for a while: to write a book on the topic of how precision is actually obtained. It's not a chicken and egg tale, as some believe.

 

[Weldingrod1]

Maudslay... and others.
Moore (IIRC) has agrest book on this subject.

Sent from my SM-S911U using Tapatalk

 

[Uglydog]

How did they build the first straight edge when there were no straight edges?

"The surface plate was designed and developed as a precision tool by Henry Maudslay and Joseph Whitworth in order to ensure the production of identical tool parts. The first surface plate was composed of cast iron. The first surface plates were sold in 1904 by the Crown Windley company. During World War II, metal was in high demand which resulted in the introduction of using granite, a non-corroding metal that is extremely hard and non-magnetic."

The Surface Plate

My work in inspection, and as a quality management system auditor, provides numerous opportunities to acquire knowledge. It also provides areas of risk for ensuring valid and reliable results.

www.qualitymag.com

I've heard that the concept dates back to the Egyptians who used water levels to algin their structures.

The 3 plate method of achieving flatness only requires organization and a huge amount of work, especially for very large items.

Daryl
MN

 

[Janderso]

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.

There was a time when the cost to ship the bed out to be reground was an option. Unfortunately things have changed.
I agree, it may be time to invest that money into the proper tools or a new lathe.

 

[m1kemex]

"granite, a non-corroding metal"

Excuse moi?

I've heard that the concept dates back to the Egyptians who used water levels to align their structures.

Maudslay... and others.
Moore (IIRC) has a great book on this subject.

Yeah. If you're after cooking recipes, there are plenty of books out there. But to understand what precision is and how it is really obtained, I don't think there is much material.

 

[Dabbler]

Can someone please point me in the right direction?

How would you scrape in a 24" straight edge with an 18" surface plate?

I don't think there is much material.

That's because Connely's book "machine tool reconditioning" has all the info already. But as one of the above posters said, just reading it isn't quire enough. I'd buy a worn out Atlas 6" or something and make all the mistakes on that first.

By using the diagonals,you can directly read almost 30" on an 18X24 surface plate.

Cheap ways to go longer:

1) buy a used large surface plate. They come up often enough. I've turned down quite a few. The larger they are, the less they cost. A used surface plate will still be far more accurate than a bad lathe bed.

2) keep an eye out for auctions and shop disposals. You might find a unicorn.

3) Look for surplus straight edges from russia. Asia have some pretty good deals for 36" cast iron straight edges,

4) Keith rucker knows a guy in PA that will grind your lathe bed, for a price. Probably cheaper than buying all the tools!

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Why you don't need a Cammelback straight edge for truing your lathe bed: the headstock and tailstock ends will be pretty true to factory spec. You need to bridge the stuff in between, and then spend 100s of hours scraping everything. A standard bar straight edge can do this, but not as accurately as a cammelback.

 

[ddickey]

His surface plate is 12" x 18". You could not do a 24" straight edge on that size plate.