Mortising bit broke

[Bryan Cramer]

I was cutting 1/4" mortises 1" deep in cherry with my Delta mortising machine and the stock 1/4" auger bit broke off about 1/4" up the shaft. I have no clue what am I doing wrong. I have read my woodworking book, 2 magazine articals, watched 2 videos online, and read some threads here on this forum. My clearance between the chisel and the bit is 1/32. My feed rate was fast enough to avoid overheating, but not too fast. I even clamped the work peice to the fence so it did not move. What am I doing wrong? Could I have faulty chisels and bits? The machine is still on warrenty so I might be able to return them but I would like some advice before I replace the bit. I forgot to mention the chisel was supported on all four sides and I had sharpend/honed the chisel.

Thanks.

[Victor Robinson]

I had the same thing happen - same machine, same sized bit. I chalked it up to not taking the time to hone and sharpen the OEM chisel/bit before jumping into a project.

[david brum]

I had this happen as well. I think it's characteristic of cheap 1/4" mortising bits. They are either thin enough in the middle to transport chips up the chisel and they break easily, or they are thicker and tend to jam (and burn) chips inside the chisel. The best solution might be to get a better chisel (made of better steel), although I personally wouldn't be shy about asking for a warranty replacement.

[Steve Kohn]

I also have the Delta benchtop mortising machine. I was using it last week and noticed the head had worked its way loose from the dovetailed ways. I snugged up the screws, not too much because the head needs to move up and down, then I realized there is no way to prevent these screws from backing out again.

Could that be part of your problem in breaking bits?

[Bryan Cramer]

There is no fault in the machine, it is working properly. Getting them replaced under warrenty is questionalbe. The company quotes "operator error". So if I do have to replace the chisel and bit how good are the Lee Valley chisels and bits? I dont want to purchase the $42 chisel(because I am still learning how to use the machine), but what about the $14 chisel?

[Kent A Bathurst]

Bryan - You get what you pay for. I can't tell you about their $14 item, but the others are great. You have to sharpen everything, and keep them sharp.

On the original problem - I did the same thing once myself. I thought it through, and here is what I decided [may have been wrong, but this is where I landed]...........I was plunging too fast, and not letting the drill bit do it's job. I would not have been plunging that fast with a bit in my drill press. I also think that I was not getting the chips cleared well enough. Both of these factors led to higher heat, and higher stresses, and it snapped.

[Bryan Cramer]

I can not get the chisels replaced. I think I will try to plunge slower (the same speed as my drill press like Kent said) even though by book says to plunge a bit faster to avoid heat build up. I am going to purchase two 1/4 $14 chisels from Lee Valley in case I overheat one from my slower fead rate. Thanks for all the helpful advice!

[Bob Lang]

Increase the clearance between the bottom of the chisel and the bit. Most instructions say to use a dime for a spacer, but that doesn't leave enough room for the chips to clear. That will lead to smoking and burning, but the temperatures don't approach what would damage either the bit or the chisel. A quarter's worth of space will run much cooler. When I tested bits and chisels for Woodworking Magazine a few years ago, there wasn't a significant difference between inexpensive chisel sets and the high-priced ones. However, the number of people responding to this with the same problem suggests that the ones that come with the Delta may have been "value-engineered" beyond usefulness.

Bob Lang

[Van Huskey]

I can not get the chisels replaced. I think I will try to plunge slower (the same speed as my drill press like Kent said) even though by book says to plunge a bit faster to avoid heat build up. I am going to purchase two 1/4 $14 chisels from Lee Valley in case I overheat one from my slower fead rate. Thanks for all the helpful advice!

I would get one of the premium chisels instead you will be better off and it comes with free shipping since it is over $40 (until the 3rd). One good chisel will last you a LONG time and always work better than the cheaper ones. If you do not have a sharpening cone you need that as well.