Bit Sharpening

[Tom Storey]

A question about sharpening the square bits used in the Monster and Clark deep hollowing systems. The bits, from 1/4 to 1/2 inch (4" length) are readily available and not really difficult to sharpen. But, at what angle do you grind the bit for optimum cutting during the deep hollowing process. I currently have the Clark system and use it 12 inches into the workpiece. I don't get much vibration but I get the 'impression' that the cutting angle of the bit could be better????

Thanks, Tom

[Steve Schlumpf]

Tom,

I have this angle edge on all of my hollowing cutters and have found when the cutting angle is somewhat sharper - the bit will dig in more than desired. I do think that using a secondary bevel makes a huge difference and highly suggest that if you are not using one - to give it a try and see if it helps.

Here is a photo of one of my 1/4" cutters. Red lines are there to give a general idea of angles used.
Bit Angles.jpg

Hope that helps.

[Bernie Weishapl]

I cut my bevels at 80* the same as my scrapers. I also put a secondary bevel on mine but do find with a 80* bevel that most times a secondary bevel is not necessary. Although out of habit I still put them on.

[Ken Glass]

Tom,
I am with both Steve and Bernie. I use 75 degrees and set a second bevel of 45-50 degrees similar to Steve's picture. I also ease the sides back a ways. ( That was Randy Pruitt's suggestion some time ago and it also prevented catches and made for a smoother tool control.) You will have less catches with a high bevel angle, but you can take plenty of stock off on the inside of a form. All my inboard scrapers have the same bevel angle as my hollowing cutters.

[Gary Herrmann]

Do the bits with the Monster rigs come ready to go or, like most things, do they need sharpening/honing?

[Ken Glass]

Gary,
Although they come ready to use, I eased the edges back for better tool control.

[Richard Madison]

'Bout the same here. Included angle of 75 to 80 degrees (tool rest on that grinder wheel is never moved) and then grind off about half the heel (hand held). Randy's bits are ground that way as delivered, so you could just set your grinder tool rest to match and leave it there.

[Ryan Baker]

I also use about 80 degrees. I have not yet found a need for a secondary bevel, but may try it.

[Tom Storey]

I just ran out to the shop to measure and I'm in the ballpark with you all at about 75 degrees. I have not, yet, knocked the chin off the bevel, but I'll try that. I think I have rounded off the shoulders more than anyone has described so maybe I don't have enough of the cutting face contacting the work piece I'll ease the curve on the nose a bit and give that a try as well.
Thanks for the replies!