||[Nov. 7th, 2007|11:49 pm]
I think I've proven that the concept of using carbide-tipped hole saws works pretty well, if a bit slowly, to cut out the disks for the next generation of pizza cutters. Two pattern-welded disks at 3" diameter x ~1/4", one test piece of bandsaw blade at 3" diameter x 1/8", one ATS34 at 4" diameter x 1/4", one band saw blade test piece at 4" x 1/8".
The drill press required quite a bit of tweaking to get everything just right. At first, the spindle driving the chuck kept coming loose, and since it was attached to the freely-turning spindle, I couldn't really get it tight enough to keep it from coming loose every so often. Finally, after it had pissed me off enough that I was no longer content to re-tighten it every 5 minutes, I used a bar of steel through the slots in the hole saw to hold the spindle rigid, then my biggest adjustable wrench to tighten it down until it was snug. It worked, now the belts were slipping (the drill press is the kind where you adjust the speed by moving two V-belts between three pulleys, giving a wide range of drive speeds.)
Since I was trying to do something pretty extreme -- cutting a slot in tool steel some 1/8" wide by ~9.4" long -- I wanted the slowest speed, lots of lube, and lots of downforce. Sadly, that was not to be. The slowest setting used (unavoidably) the smallest drive pulleys, and the 1hp motor would just spin that pulley freely, potentially burning out the belt if I let it. I tried tightening the tension, using belt dressing, but I just couldn't get the torque from the motor to the saw. After trying a few different configurations, I settled on a setting not in the chart -- 2nd smallest pulley on the motor going to the largest pulley on the middle transfer pulley setup, and the 2nd belt going from the 2nd smallest pulley on the middle unit to the largest pulley on the spindle unit. I could do this because I really need to replace my belts, they are worn and stretched enough that I could get them to fit like that. Fortunately, belts are cheap.
I now had enough torque transferring to the saw that I was starting to stall out the motor, which is where I wanted to be. I used a combination of a water-soluble oil machining lube in a spray bottle, and when things started to get really gunked up, nuclear grade drilling/tapping lube. Hey, it was only $.50 more expensive than the non-nuclear grade, so I figured what the heck.
The 3" saw, designed for working with metal, worked fine. The 4", which explicitly says on the box "not recommended for use on metal," needed some modification. Hey, I got it cheap on ebay, which didn't mention this wasn't a metalworking carbide-tipped hole saw. The basic problem is that there were too many teeth -- I could make a cut in the steel, but it was taking forever, generating a lot of heat from friction, and kept stalling out the motor. I gave it a while just to see how long it would take, and after about 45 minutes had cut about 3/32" into the piece. I then flipped the work over (this was in the 1/4" ATS-34), took the hole saw over to a grinder, and ground off every 4th tooth, as well as cut a couple of extra-deep gullets to assist in chip removal. Cutting through the rest of the steel took about half an hour using the modified saw. I may cut out some more teeth, since friction still seems to be the limiting factor. Or I could break down and spend the $120 for the right saw. Or, once I've got some income from this hobby, maybe buying that lathe I've been advised is the right tool for the job.
Anyway, I've mocked up a jig for griding the disks. Since they already have a 1/4" hole in the middle from the cutting-out process, I took some bronze bearing material, about 1" long, with a 1/4" bore, and some 1/4" rod,and made sure that I had a decent slip fit, then using some hose clamps, I attached the bearing to a 4" C-clamp. I then bent the rod to give me some leverage, and have used a die to thread the end that will be holding the disks. I expect that I'll find the 1/4" rod too flimsy, and I doubt the hose clamps will last very long under the stresses of grinding, but if the proof of concept works, I can make a new one using 3/8" or thicker, end-drill the rod, and use a decent bolt to hold on the disk, and attach the bearing with some good braze (somewhere I've got a tube of commercial silver braze) or bolt it on with a flange. Or maybe JB-Weld, haven't really decided yet. This gizmo will attach to the work rest on my bigger belt grinder, at least for now, which is pretty adjustable in terms of angle and distance from the contact wheel until I can figure out how to make it work.
I've got pages of designs for pizza cutters in my notebooks, and soon I'll be at the point where I need to decide what the cutter for each wheel will look like. While part of me really likes the designs with lots of cut-outs, with the milling machine dead that's probably not the best choice for now. Then again, now that I have the drill press tuned in, there's alwasy the "lots of holes" look. Hmm.