Hollow chisel mortiser chisel question

[Scott Rollins]

I just bought a new steel city hollow chisel mortiser. I made some test cuts and the mortiser works great but the chisel (1/4) deflects to the open side of the chisel about 1/16" when cutting. I was going to try sharpening the chisel, but I know that most of the time the cutting implement included with a tool is junk. So which brand of hollow chisel should I buy? I looked first at the Lee Valley "premium set" ($115) I also saw they had an Economy set for about $60. Are there any recommended brands on these or ones I should stay away from?

[Dick Bringhurst]

I use the Lee Valley set ($60). I also cut the ends of the mortise first, then the center portion and don't have to worry about an angle cut. Dick B.

[Rod Sheridan]

Hi Scott, the deflection may be caused by bending of the chisel, or the wear strips on the ways need adjusting (if your machine has any).

I normally plunge the end cuts first, then plunge the remainder as follows;

- plunge remaing cuts about 1 1/2 chisel widths apart so that all sides of the chisel are supported

- plunge the remaining aproximately 1/2 width spots, this way the chisel isn't having to accept any sideways asymmetrical forces

It makes for a nice clean mortise with no sideways thrust on the chisel.

One other tip is to hone both the inside and outside of the chisel to keep it sharp, and I use a dime as a thickness gauge to make sure that I have enough auger bit to chisel clearance as follows;

- insert a dime between the shoulder of the chisel and the chisel holder, tighten chisel locking lever, remove dime.

- insert auger bit all the way into chisel, tighten drill chuck.

- loosen chisel locking lever, insert chisel all the way into chisel holder, thus setting auger bit/chisel gap at one dime thickness.

Have fun with your mortiser, they are great machines....Rod.

[Jim Becker]

A set of sharpening hones will get those stock chisels working much better. Also try feeding slower and cutting a series of unconnected plunges across the width of the mortise before clearing out between them with the chisel/bit. Be sure that the bit, itself is just below the bottom of the chisel...it's what does the cutting, not the chisel which is just to clean and square the hole.

[Scott Rollins]

I cut the ends of the mortices first and then stepped across leaving a bridge of material between the nice square holes. It was the bridge removal where I noticed the deflection in the direction of the chip chute on the chisel. The dovetail ways are very ridgid (tested with an indicator and saw less than my indicator would read side to side). Also the wood looks torn int he bridge areas and nice and clean in the initial plunge areas. I think I will try sharpening and honing the chisels before buying new. Thus the next question..exactly how does one sharpen the end of the chisel with the cone shaped sharpener? Is the round shank for mounting in a drill or is it for spinning it manually? Sorry for the newb question but this is my first Hollow chisel mortiser.

[Jim Becker]

Scott, I use the cone-hones :) in my cordless drill...

[Mike Cutler]

Scott

The 1/4" chisels don't have a lot of material mass to them. You might see more deflection with them than with say a 1/2" chisel. (I bent a 1/4" in Jatoba one day.:o)
To sharpen the chisel use the cone shaped sharpener in a drill, set to slow speed to avoid overheating the edges, to hone the inside of the chisel, and a stone to hone the outside of the chisel. Those chisel edges need to be very sharp, especially the corners.
Don't forget to sharpen the bit. Make sure that the leading edges and flutes of the bit are sharp. The better the drill is cutting and removing waste, the easier work the chisel has to do.
Don't let the waste material fall back into the area that is being mortised. Get your vac right at the chisel to remove waste as soon as it is ejected.

I cut the ends first,and then step across the middle, overlapping the cutter by about 2/3ds. The wood supports the chisel, so the more wood it's cutting the more support it has on the sides of the chisel. I don't leave the bridges for the same problem you encountered, wandering and ragged edges. Sometimes it's unavoidable though.

Not all hollow chisels have the same angle of grind to them. Clico's for example have a different grind than Delta's. It's not really a problem, but the sharpening equipment has to accomodate the different angles. Something to be aware of.

[JayStPeter]

I suggest you look here http://blogs.popularwoodworking.com/editorsblog/Hollow+Mortise+Chisel+Tuneup.aspx

Jay

[John Thompson]

Mike Cutler nailed it about 1/4" chisels being a bit flimsy and that includes the Lee Valley and Clico's from Sheffield, England.

And Jay St. Peter just posted a link to one of the few (I have not seen one in 36 years before the link article did the test) hollow mortise chisel test and results. And you will find it interested, especially the results.

I run CMT's which are not in the test, but are excellent in the mid price range. The cone's Jim B. mentioned are excellent also as about all chisels come with grind marks and need to be honed. The Lee Valley and CMT actually come better machined than the expensive Clico's that aren't that expensive in England.. but outta sight here.. go figure?

Sarge..

[Bob Lang]

The mortise chisel test article was in the Spring 2007 issue of "Woodworking (http://www.woodworking-magazine.com/)" Magazine. Back issues are available either in printed form or as a PDF download.

Bob Lang