Scraping materials other than cast-iron

[AgnewBlues]

A question for the scraping experts here: Microscopes and other optical instruments often have dovetail slides made of bronze, brass, or aluminum (sometimes hard anodized, but often not). They sometimes have milled slots for lubricant retention, but often not even that. They are usually not scraped. In some larger units, one part of the dovetail slide is cast iron and the other part is bronze. Sometimes steel on bronze. Or even cast aluminum on bronze. Often with no slots or scraping (no lubricant retention provision).

While the forces and mileage are usually low, after decades they wear out. Would scraping softer slideway materials (bronze, brass or aluminum) be beneficial for their operation and longevity?

Does anyone have any experience doing so? Would the technique and principles be the same as for cast iron?

The three main issues I can imagine are as follows:

1) Softer materials have a tendency to throw burrs or horns around slower speed cuts, which may prove detrimental to overall surface accuracy.

2) Such slideways are usually quite small, with very limited space to work.

3) In some cases, the original selling price point of the instrument would not have allowed for scraping, even if it would have been beneficial.

I am interested in this topic, both for reconditioning such instruments, but also for making some new slideways for use in such applications.

All opinions and discussion would be greatly appreciated.

 

[Richard King]

I have never scraped a Micro-scope slide. If I did I would make a thin blade hand scraper and probably a short handle and use my arms. I would scrape it the same way and start out lowering the center 40% as it is probably high in the middle. If your scraping softer materials, you would grind the blade tip rake at 10 deg's or more, the softer the steeper. The blade could be HSS and sharpened on a slip stone. Probably 1/2 wide x 1/16" thick or less. De-burr with a dull file or thin tapered slip stone. You could try pull scraping to lessen the burr or scoop scrape. No oil on the slides are no surprise as they are so slow moving no change of stick slip.

 

[AgnewBlues]

The blade could be HSS and sharpened on a slip stone. Probably 1/2 wide x 1/16" thick or less.

Many thanks for your informative reply, Richard!

Just to be sure, I am assuming you would be cutting with the 1/16” face? Kind of like a parting tool blade?

 

[Richard King]

Just like a regular scraping blade but thinner, so it could fit at the bottom vertex of the dovetail

 

[Conrad Hoffman]

I think I've seen old optical instruments with scraped slides. I've had no problem scraping aluminum and brass, though mostly as an excercise rather than some grand purpose.

 

[AgnewBlues]

Just like a regular scraping blade but thinner, so it could fit at the bottom vertex of the dovetail

Thanks for the clarification! In that case it may have to be a bit narrower than half-inch, as some of these slides are only around 2 inches wide, or even less.

 

[AgnewBlues]

I think I've seen old optical instruments with scraped slides. I've had no problem scraping aluminum and brass, though mostly as an excercise rather than some grand purpose.

Any photos to show? I’d be very much interested to see what it ends up looking like.