Cutting M2 Knife Steel
Is burning the steel while cutting a concern? January 16, 2004
What is the best (low cost) way to cut m-2 knife steel to length without burning the edges? Also, any tips for squaring the ends? Currently I use a chop saw with a metal cutting blade. It burns the edges and has trouble making a square cut. I don't have the time to get them cut by a second party machine shop. I have seen after market grinder attachments that can square knife steel but they cost $1000.
(Solid Wood Machining Forum)
We use a Makita 14" metal cutting chop saw with a 30 grit triple reinforced wheel that we have custom made specifically for cutting knife steel. It is quite important to use a chop saw made specifically for cutting metal, as opposed to a wood cutting chop saw fitted with a metal cutting blade.
The center reinforcement is the full 14" diameter, and the other two outer reinforcement meshes are about 7" in diameter. This offers two advantages over conventional cutoff wheels. First, the wheel is more rigid and cuts very square. This is due to the triple reinforcement. Second, the wheel not having the outside reinforcements the full diameter cuts faster and cleaner, greatly reducing the burning.
We use a special grade that really cuts the knife steel like butter. That being said, I have personally cut a variety of different manufacturer's steels. I like the way WKW's M2 High Speed Steel cuts. It is a good Rockwell hardness, and more importantly, is very consistent, making both cutting (and balancing) a dream rather than a chore! Choosing the right steel to compliment the wheel is just as important in this operation as in your choice of profile grinding wheels. Match the wheel(s) to the steel.
We have used the same chop saw for over 15 years and it still does a great job. We have literally cut hundreds of bars of steel with this machine with excellent end results.
Don't worry about it. The burning on the edge as you're cutting the stock has nothing to do with the cutting edge of your knife. The squaring? Take a razor blade and pick a corrugation. I use the third from the back. Use the blade as a straight edge. Slide the knives in the head until they hit the straight edge. Then lock 'em in. That way, everything is set the same.
M-2 isn't particularly heat sensitive. The blue zone that marks the kiss of death to a plain carbon tool steel plane iron means zip to a moly tungsten HS steel. Just cut it and don't baby the cutting wheel. You have to actually wear the wheel a trifle in every cut so fresh, sharp abrasive is exposed to make a clean, cool cut. If the abrasive chop saw (never use a wood cutting chop saw for this, as the loose abrasive will quickly ruin it) is set up correctly, it will cut square. You may have to tweak yours. As for end registration, the usual practice is to grind the knives to profile with the registration edges flush to the machined face of the head.
You are talking about corrugated M2 steel, right? If you are, then it doesn't matter if it's square or not. When you lock in the head and grind the knife it will all work out, unless you are way out of square. I don't have that out-of-square problem anymore. I just took a short length of corrugated steel I had laying around and drilled two holes in it, then attached it to the chop saw. He he… so the steel I'm cutting locks into the corrugations of the steel attached to the chop saw - perfect straight cuts every time. And If I'd been a little smarter when I did it, I would have used a longer piece of steel and cut it off so I have a marker for where the cut is going to be and make it easier for lining up my cut lengths. Have fun cutting your steel.
From Dave Rankin, forum technical advisor:
Some basic information from experiences in the field. If you are using any type of axial constant dimension, then you have no concern about the minor burning that occurs from cutting M2 steel with most any reinforced cutoff wheel. For example, if your burn is 1/8" wide then the most that you will have damaged the steel is double that or 1/4" wide. The damage that occurs is not loss of the temper but a fracturing of the steel. Unless this area is within the cutting area of the tool, then you need not worry. I offer a special cutoff wheel for cutting M2 steel, but for most companies I recommend that you go to a home improvement warehouse and pay $5 or $6 for a reinforced wheel. It will do the job well enough for most types of production shops. You can also add a little bit of wax into the wheel and this can help to lubricate the cutting action.
As for the question about squaring, this I think is more important than most. If the pair of knives are square and cut to the exact same length, then balancing of the knives is very quick and much more permanent. How often have you cut knives, ground them, run them on the moulder, then had to step the knives out of the head? If the knives are square, they are easy to re-reference to the edge of the head.
A couple of weeks ago, I was asked to cut, square, balance and grind 10 pairs of 4" knives. I used a reinforced cutoff wheel to cut them. I then used the MSI knife squaring device to square all of the edges and grind them to an exact length. I then built up the heads and ground all of them. Total time for the entire project was under 2-1/2 hours. The squaring device saved me at least an hour if not more and the tools are exact length.