Mortiser chisel size

Ty G

Well-known member
I just ordered a powermatic benchtop mortiser (one of those.. get the best I can afford things).  What size chisel (mortise) do you guys use for highboy legs?  What are the most commonly used sizes in your shop?

Many thanks, Ty
For general use I stick with the 3/8" chisel.  For narrow mortises, such as a splat, I go down to the 1/4".

Rarely use anything bigger, and for a large mortise like a bed rail I usually just go multiple passes with the 3/8 but it would make perfect sense to use a larger bit.

You might want to consider Forrest City chisels and bits.  They reprersent that they are a level that is above the bits sold with the machines, and offer replacements/substtitutions for a number of mortiser manufacturers brands.

Ty- By far the most common mortise size in early work is 5/16. It's 1/3 of 15/16 so the shoulders are the same width. So evreything's 5/16 tenon, 5/16ths in from the face. I've never seen a chair that wasn't this way except on the splat, and I can't remember a case with anything larger. Bed rails are the exception, as was noted.-Al
For cabinet work all I use is a 5/16" bit. I'm a hobbyist, not a professional,  so the bit's not used daily. But I have been using the same $12 Chinese-made Woodcraft-sold bit for 6 years. When it dulls I won't worry about sharpening it, I'll just get another one.

Howard Steier

I have the same bit from Woodcraft that I bought over 5 years ago and it is not showing any signs of dulling.  I'm a professional so mine is used all the time.  I agree, when it does dull just buy another one.

Sometimes a more expensive name brand does not mean it is better.

Dennis Bork
Antiquity Period Designs, Ltd.
I wasn't happy with the chinese bits. I tried Lee Valley's best japanese ones and wasn't happy with those in hard woods. I bought some forrest bits and couldn't be happier. If you do check them out you will notice they have a different design. They are not really drill bits, they are twisted chisels.

They work so well I though something was wrong the first time I used one, I saw chips coming out but there was no effort in pushing the head down. Turns out is was working fine. and after running a 6" mortise the bits are warm but you can still touch them, and heat is the enemy of tool steel.

If you do need to sharpen them lee vally sells a set of cones for sharpening. They worked quite well the one time I used them.
I have to agree with Al and Howard.  After teaching 35 years in a public high school shop, 95% of the mortises we made were 5/16"  and the other 5% 1/4, 3/8" or 1/2".  And it seemed that the cheap import bits lasted fairly well, and even could be touched up with an auger file if it wasn't blued.  And we're talking about kids mortising non-stop, class after class!
The comments so far seem to indicte a wide range of satisfaction with imported bits for a mortiser; ranging from rather complete satisfaction to the opposite.

One very large problem with imported items made of metal is that, while it is easy to check for appearance , it is far more problematic to be sure that the maker consistently employs the right "metalurgy" technology  and raw materials - the processes that assure that metal parts end with the best physical properties - because it is more or less invisible, and we are in the habit of trusting that manufacturers have knowledge of this which they incorporate in their tools. It is the assumption that the manufacturer employs the appropriate steel and best processes that enabled once famed manufacturers like Stanley or Buck Brothers in the old days to build strong reputations which have made some of them the gold standards, for chisels, planes, carving tools, etc.

With tools from "virtual"  manufacturers, it is not possible to tell easily which ones manufacture to the best prac tices, and with consistent quality.

I believe this explains the wide varierty of experience. You may have wonderful luck with import, or you may not.