Thread: My First Boomerang Saw: Fixing a Compound Bend

A customer contacted me recently about a saw that I'd sold him a while back. Seems that it bound in a cut and the blade was bent. I asked that he send it to me for repair or replacement of the blade. Turns out it's No. 31, the first D8 saw I sold and the second one of this type that I made.

No 31 in the shop 100916 035.jpgcloseup of handle.jpgCloseup of SN.jpg


Here's a picture illustrating the bend in the blade. The black arrows denote nodes where the toothline crosses over the center. The red arrows indicate the centers of the two bows of the compound bend.

No 31 compound bend annotated showing bend nodes.jpg

Here are the tools used. The picture on the left shows a Sharpie for marking the blade, a split nut driver and an insertion/removal tool for the handle bushings. The center pic is my personal No. 3 sawsmithing hammer and finally my Peter Wright anvil. I someday hope to make sawsmithing anvils that are as useful as this one.

dissassembly tools.jpgNo 3 sawsmithing hammer.jpgNo 31 in the shop 100916 004.jpg


On disassembling the saw I noted that the bushings showed polishing from the blade. This tells me that they're doing what I intended them to do - hold the saw blade firmly in place and prevent damage to the screw shanks.

bushings showing signs of having done their job.jpg

The next step is to mark the positions of the nodes defining the bows by sighting down the blade and marking the positions where the toothline deflects across the midline.

No 31 in the shop 100916 020.jpg

Here's the blade with the bows marked.

No 31 in the shop 100916 018.jpgNo 31 in the shop 100916 015.jpg


Now the blade is hammered about an inch above the toothline between the marks on the convex face of both bows. It's important that the blade, particularly finished blades such as this one, and the faces the hammer and anvil be free of contaminants - I've found that seemingly innocuous things such as saw dust will leave dents if present at the point of impact. The face of this anvil isn't perfectly smooth of course but it's smooth enough that the shallow dents don't have a deleterious effect on the surface of the blade. It's also important to use a hammer with a radiused striking face to avoid dents from the abrupt edges present on some sawsmithing hammers I've seen for sale.

hammering bend 1.jpgHammering bend 1 shot 2.jpgNo 31 in the shop 100916 016.jpg


After several rounds of hammering and checking the blade straightness the saw is restored.

No 31 straight again 2 .jpg

Now to remove the scuffs from the hammering. I use this Dewalt 1/4" drill because it has a 4000 R.P.M maximum speed. The abrasive is a 180 gr. combination flap wheel from one of my favorite companies, 3M.

Dewalt refinishing drill.jpg3M flap wheel.jpg


After polishing and reassembly the saw is ready to go back to it's owner.

No 31 before repair side shot.jpg