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Slitting saw update

I slit the first set of 2″ deep slots for the flat blade, and the angle blade today. Here’s my findings:

  • It is possible to do the entire depth in one cut. However, it did seem to go a bit smoother with the pilot of the 3″ carbide blade.
  • You must enter to full depth very slowly or the blade will stick. I went about 1/3 as fast going in, as slicing across.
  • It worked best at 85 RPM. The equation I found here (along with a few other good tips) would suggest RPM’s of about 43. Our machine could do 36, 54, or 85. At both 36 and 54 RPM’s, the blade didn’t have enough momentum to prevent it from getting stuck easily.
  • Using Mistic Metal Mover, and Boelube really helps to make it cut. I applied both liberally when the blade started to make extra noise.
  • When the blade sticks, sometimes it works to back it off a tad and try again. Sometimes you need to take it out all the way.
  • When something snaps, its almost always the bolt. It pays to take it out even if it seems to tighten up OK. A few times, it snapped, but still held lightly together. Had I continued machining, the bolt would have fully broken off inside the threads and been very time consuming to remove.

Tomorrow, I’m flipping it up and will cut out the flat blade and part of the angle blade.


Using the slitting saw

I began to use the slitting saw yesterday, and, Boy, is it tough. The issue is that the arbor I bought doesn’t have a keyway, so if the blade catches, it still spins the top half of the arbor, but not the bottom half. This means that the bolt tightens and snaps. I broke 4 bolts yesterday on the arbor. Luckily, we had extra bolts at the shop we could use. If you plan on using an arbor without a keyway, I suggest you head to your local hardware store and pick up 5-10 extra bolts when, not if, you break one.

The solution for not catching the blade would be to go at a more constant rate. However, since our machine doesn’t have an auto-feed, it is really difficult to keep a constant speed. I’m gonna try to rig something up today with a drill, but given the high torque and low speed, this will likely be impossible.

Another issue is, since the blade I bought is High Speed Steel,  I have to be really careful about using it on the material which has been torched, as this could dull the blade really fast. My answer to this was to do one pass with the carbide blade we have on hand to break thru the harder steel. The problem is that this took HOURS. Hours to cut a .5″ deep slit in 18″ of material.

The end of the first slit.

I reccommend doing a test cut in some of the material which will be removed. This way, you can understand the limitations, and if you will need to make shallower cuts.

A test slit to double check the height is correct on the blade. (>1" away from edge)

I’ll likely need to do more than one pass to get the blade to the proper depth. In my trial piece, I found I could only cut about 1″ deep with the 6″ blade without catching the blade.

Fixing the arbor

When the bolt snaps, this could be a difficult repair. As I had 4 snap on me, I had to try a vareity of techniques to fix it.

If you’re lucky, the bolt will snap so that you can simply grab the threaded half with pliers and twist it out. Try this first.

If there’s still some thread sticking out, but you can’t twist it out, you can weld a nut to it, and use a socket to get it out.

If the bolt breaks off inside the threads, the only solution I found is to drill it out. Find out what size drill you would need for that tap and drill with that bit, being really careful not to let the bit get off centered, as this could destroy the threads. I suggest doing this in a lathe if possible.

The worst case scenario, which happened to me, (along with everything else listed) is that somehow, the bolt

The bolt whose head we had to drill out.

doesn’t break, but the threads strip. The bolt will twist, but won’t come out. In this case, you have to drill the bolt out from the head. The problem with this is that the bolt is free to spin, and will start to spin when you drill it. It took a really fine touch (Jimmy’s) to drill it out. He had to come up on it lightly and back off when it started to spin again.

Drilling out a bolt. You can see the threads came off onto the drill bit.

Breaking the bolt is a pain to fix, so be really careful the blade doesn’t stick. If it does, shut the machine off ASAP. Don’t bother with trying to back off the table. Shutting off the machine will be much faster, and safer for your bolt.