Biax replacement blades

I have acquired a Biax power scraper and after finding out the prices of replacement blades I have decided to make some for myself. I want the 150mm length blades and I will braze on carbide blanks and radius them. However I do not know what type of steel they are made of and the thickness and width they should be. Can they be made out of mild steel or does it need to be tool steel. Also I have noted that the 150mm blades are thinner than the short ones I have and thinner than the blades with the indexable insert heads.
Any advise or dimensions would be greatly appreciated.
Thanks

Skipd1

Mild steel will likely bend fairly quick, especially where they mount to the scraper. I'd go with a tool steel. Lengths vary, but they're roughly 1/8" x 3/4" stock with an open slot on the end to insert into the scraper.

I'd buy one so you can have it to compare with whatever you make. They are pricey, but unless you're running your scraper daily, they should last a long time (sharpening included). They'll likely last longer than a milling cutter of comparable value.

The exception would be when I dropped a #25 blade and the carbide tip broke in half. Might still try to braze it back together and use it for rough-roughing.

It's been suggested here that old saw blades make good blanks. I have some .1 thick power hack saw blades saved for the ones I want to make.

I've made a few using 1018 steel, no much bending issues.
However, I find myself using almost exclusively the Biax insert holders with the shaft significantly thinned down.

One important thing when making the blades is the width of the attachment point: there should be as little side play as possible, otherwise the blade will rotate left-right while scraping. Theoretically not a big deal while roughing, but enough imprecision in finishing to land a stroke in the wrong spot (and possibly, ruin the attachment socket as well). If I recall correctly, the socket is 20 mm wide (0.95 mm wider than 3/4").

Paolo

ewlsey said:

It's been suggested here that old saw blades make good blanks. I have some .1 thick power hack saw blades saved for the ones I want to make.

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That is not a bad idea!

It is quite easy to braze a carbide tip to a piece of steel. I have built quite a few hand scrapers with braze on tips. As for steel i bought a piece of 3/16" thick spring steel and thinned it down to get proper spring. I have not tried to make a biax blade as they are commercially available.

Thanks everyone, I too have made a few brazed carbide hand scrapers and they work great. I am currently making a slow speed diamond lapping machine similar to the one made by the How to Make a Slow Speed Grinder Part 1 - YouTube.
I think I will try to make one out of mild steel and one out or tool steel and see how it works. Thanks for the advice on the correct width for the mounting point area. Good advice
Thanks

Skipd1

I am also somewhat confused to the different radius of the blades and their widths. What radius is best for roughing and what size for finishing and scraping out to higher point/inch? Is the 30mm radius for finishing and the larger radius for roughing?

skipd1 said:

I am also somewhat confused to the different radius of the blades and their widths. What radius is best for roughing and what size for finishing and scraping out to higher point/inch? Is the 30mm radius for finishing and the larger radius for roughing?

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Wider blades (#25 to #30) have a larger radius, producing a wider cut for roughing. Mine are shorter giving less flex so they dig in more but the scrapes are not as fine. The wider blade also puts the corners further out so you are less likely to scratch while you go wild roughing a surface down.

Narrower blades (#10 to #20) offer better visibility and have a smaller radius, producing a narrower cut for finishing work. Tend to be longer with more flex so they don't dig in as hard.

Especially when talking about power-scraping, I think that it helps reasoning in terms of the sector of circle between the corners of the blade and the (imaginary) center of the circle describing the radius of the blade.
In essence, between wear on the harder steel pads and blade carrier (allowing a slight rotation of the blade compared to the body of the power scraper) and some tilt introduced in holding the power scraper, there is some "tilt tolerance" of the blade.
If the tilt is excessive, you dig in with the corners of the blade.
The narrower is the angle of the sector of circle, the less the tolerance.
That's why it's a waste to grind a steep radius on a large blade and why you would use only 30mm and wider blades for radiuses 90 mm and wider.
Especially when you're starting using a Biax, I strongly suggest you use no more than 60mm radius even for roughing.
Especially for finishing, it is very important that the shoe holding the blade is properly adjusted to remove any play with the harden steel ways ( if you have uneven wear on the ways, perhaps it's time to replace them).

Paolo