Something to replace band saw rubbings?

[tomwalz]

Something to replace band saw rubbings?

I attended some training over the weekend. As part of it there was a lecture on the importance of good band saw rubbings.

If you are in a saw mill and need new a band saw blade you take a paper and pencil and do a rubbing of a section of a few teeth of the old band saw blade. The saw blade manufacturer then uses this rubbing to make the new blade. Many of these rubbings are not clear and sharp enough.

Is there a better method to get an exact size version of a band saw blade in two dimensions whether on a piece of paper or digitally?

I am looking for a simple, readily available, inexpensive solution.

Thanks,

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[btrueblood]

Take a shadowgraph image using diazo (blueprint) paper? Lay the bandsaw against paper, expose to sun or other UV source, then put the paper in a closed box with some ammonia. Or lay a chunk of sawblade on the platen of a photocopier.

Supposing you don't want to dismount or cut up the existing blade -

- take a digital photo of blade with a steel rule next to it; import image into Autocad or whatever, and trace the outline directly into CAD lines.
- take an impression in clay or wax or "repro rubber" (basically a low-shrink silicone RTV), and digitally reproduce the image by any of the above methods.

 

[KENAT]

Similar to Btrue's second idea use the stuff dentists use to make casts of teeth for crowns etc. (maybe his name is the propper name for the stuff).

Similar to Btrue's first idea but use graph paper or a similar checkerboard as immediate back drop.

3D scanner.

http://en.wikipedia.org/wiki/3D_scanner

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[btrueblood]

Kenat,

I've been told that the brand name "Repro Rubber" is very similar to the dental casting material; we tried to get our paws on the dental stuff and were told we couldn't get it without a prescription - not kidding, and you are probably as dumbfounded reading that as I was being told it over the phone from a dental supply house. The brand name stuff we use for doing inspections is expensive, I want to say $300 US or so for about a pint of material, but it's been awhile. There are similar casting products, advertised as "low shrinkage" available from McMaster, that would probably serve as well. For an industrial repro process, I would just make a few castings to calibrate the shrinkage, then adjust accordingly in the CAD file.

But the digital photo method I think would be quickest and easiest. Another method I've seen used for photos is to put a $1 bill against the part, obscuring the serial number, and take the photo that way. The benefit there is that everybody has a $1 bill in their pocket(*), so there's no running around to find a scale or grid paper, and there's no discussion about whether the picture was taken against 1/4" grid paper or 0.2" grid, cm scale or inch, etc.

(*)Whoops. Except me, today, just a $5.

 

[KENAT]

OK, so glue a quarter onto the checker board within the field of view;-).

Interesting what you say about the dental molding stuff, I swear that's what our QA dept used back in the UK. Hard to believe it's more difficult to get here in the 'land of the free'.

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[btrueblood]

Dunno, it was one attempt. I'm sure you could procure some, but it might be a cash-only transaction, in a dark alley somewhere. I mentioned it to my dentist, and he told me what he pays for the stuff, can't remember, but it sounded more expensive than the industrial version, I'm sure because of the extra paperwork to verify that it's FDA approved.

 

[KENAT]

Plus there may be some chemical constituents that are fine for external use but you don't want in your mouth for extended periods I suppose. (If the market is big enough to warrant different versions of the same stuff.)

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[MikeHalloran]

Point of reference:
Exposing diazo paper properly takes about 15 minutes using a typical desk lamp or machine tool lamp. ... of course they must be fluorescent lamps. Sunlight works too, but it's not always found near a bandsaw.
The other limitation of using diazo paper is that almost nobody stocks it anymore.

Something else came to mind: Carbon paper. Lay plain paper against the blade, then carbon paper, then some more plain paper, and rub, say with a Pink Pearl.
Problem: Almost nobody stocks Pink Pearls or carbon paper anymore.

OR,
Lay a piece of plain paper against the blade, and spray paint the blade against the paper.
Many outfits keep _some_ kind of aerosol spray in stock.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

If you are in the business of sawing would you not have a spare blade to use for a sample for a new one?

Ted

 

[MikeHalloran]

If YOU or I were in the sawing business, of course we'd reorder before the last blade broke. ... but I have worked for a lot of outfits that ran so lean they wouldn't keep anything in stock. ... or keep a record of what they bought. ... or photograph the new part before installing it. Some people are just way smarter than us.

Mike Halloran
Pembroke Pines, FL, USA

 

[tomwalz]

Yes, yes you would.

You would have several since you change them every 4 or 8 hours or so. You would have extras since they sometimes get beat up. Sometimes the good ones and the spares get beat up in the same shift.

However these blades are customized in the mill. They are very expensive to physically transport.

Here is the official answer from Norm Brown, Regional Manager for Simonds.

Bandsaw rubbings
Tom,it is the most accurate form of duplication available with the least
amount of complexity or tools, any one can do it with a sheet of paper
and a dirty finger. We do have other ways available like the VariDesign
program that is free to every one , it is on the Armstrongblue website.
We discussed scanners etc. but the rubbing is easy and we (Simonds
convert to DXF

So Simonds does it this way because some of their customers like doing it this way.

There was a discussion at this meeting of mills that want blades to last forever and that want filers to repair wrecked blades. Other mills are more careful of staff time.

The big problem is that the steel only holds up so long. We can make ceramic tipped saw blades but they would still need to change saws every so often because the saw plate does not hold up.

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.