Slitting saw sanity check, please?

[woodchucker]

OK, thank you for clarification.

However, that unfortunately doesn't say much about what I'm most curious about,and what will help anyone else looking for numbers, the feed per tooth.

When I feed manually I still keep track of my speed (by for example making sure I turn the crank once per second which is 5mm on my mill or 300mm/min or about 12ipm). Perhaps that's because when I was learning machining I was thought to calculate my feeds and speeds then run with these and adjust them further. So there is always some specific numeric feed speed I'm shooting for when feeding by hand.

As for making chips not dust, it's a bit relative. When I first saw the "chips" it made at 300mm/min they were only barely bigger than dust. At 60mm/min they were quite close to dust, but still one could take them between the thumb and index finger and feel/see individual chips. Have a look at this photo:
View attachment 447377
Those chips are made at 60mm/min,they don't appear that much different from these that were made at 5x the feed speed:
View attachment 447378


As for the surface speed you mentioned. It is significantly faster than recommended for hss in steel.(even free machining steel) I'm interested in how much of slitting do you do at that sfpm? Are we talking about an odd screw head once per year, slitting one part a couple of inches long from time to time, or running meters of cuts? Probably, not meters of cuts... Everyone that uses hss at a home shop knows what happens when you run hss too fast. It cuts, it throws beautiful blue chips, for a short while, then the cutting edge dissapears and you have to resharpen it. It is perfectly possible to run it fast for short amounts of time. If it has no opportunity to overheat (due to a short cut for example) it may be fine.

The usual recommendation is 20m/min up to 40m/min in Surface speed is quite flexible as long as your feed per tooth (in case of it being low) and cooling (in case if it being rather high) are adequate.



Are you perhaps confusing the surface speed with the feed speed?

Three of my parts with a total of 3m (9ft) of slitting saw cuts say 25m/min is absolutely a correct surface speed to run them. It is exactly 75ft/min. However you're going to be perfectly fine running it from 0m/min up to ~40m/min.

You may run them slower or faster within reason as any hss tool, but this is my recommendation based on my recent experience of using it.

I stand corrected, I thought you meant 25mm and feed ..

 

[Huub Buis]

Are you perhaps confusing the surface speed with the feed speed?

No, 79 m/min is the actual speed. I have a lightweight (120 kg 240 lbs) manual mill. It is powered by a DC motor and has a low/high gear. Even in the low gear setting, the torque at low RPM is limited. Running at a higher RPM prevents stalling the motor. So
In general, I only use 2 slitting saws between the yearly tool sharpening. When possible, I use the band saw so I don't cut that much using slitting saws. Most of the time, I use the slitting saw on 6..10 mm steel. I guess, I only cut a few (3..5) meters a year.
The feed depends on the chips, the torque to turn the handle and the smoke (to fast) that comes of the slitting saw. I guess, I turn the handle once every 2 seconds, 60 mm/min, 0.15 mm/rev, 0.002 mm/tooth. Seems dust! I will measure the next time I cut steel.
On the CNC lathes all turning using HSS tools is done at 30 m/min in steel, never faster. Carbide Inserts are run at the recommended max speed but some times way faster (turning Gear cutters) for a better finish.

 

[Flynth]

No, 79 m/min is the actual speed. I have a lightweight (120 kg 240 lbs) manual mill. It is powered by a DC motor and has a low/high gear. Even in the low gear setting, the torque at low RPM is limited. Running at a higher RPM prevents stalling the motor. So
In general, I only use 2 slitting saws between the yearly tool sharpening. When possible, I use the band saw so I don't cut that much using slitting saws. Most of the time, I use the slitting saw on 6..10 mm steel. I guess, I only cut a few (3..5) meters a year.
The feed depends on the chips, the torque to turn the handle and the smoke (to fast) that comes of the slitting saw. I guess, I turn the handle once every 2 seconds, 60 mm/min, 0.15 mm/rev, 0.002 mm/tooth. Seems dust! I will measure the next time I cut steel.
On the CNC lathes all turning using HSS tools is done at 30 m/min in steel, never faster. Carbide Inserts are run at the recommended max speed but some times way faster (turning Gear cutters) for a better finish.

My comment was directed to you. It was directed at @woodchucker.

This is how it looks on my screen:

And BTW, he did confirm that yes, indeed he thought I was talking about feed speed when it was surface speed.

I'm not doubting you're running your hss saws over the recommended surface speed for hss. Every one of us did that at one point to a hss tool and each of us knows what happens when we do. The edge lasts a fraction of the time it otherwise would. There are certain things that can be done to delay it (use cobalt hss, light feed, flood coolant, high lubricity oil etc).If it works for you that's great.

I too have a small mill like that (in addition to my big horizontal mill). My mini mill too has a high and a low gear and a DC motor. I believe the motor is 1000W. It doesn't have a lot of torque at low rpm, but still before I got the big mill I did use it at 100rpm to drill large holes, use a fly cutter and other things (only very shallow cuts with a fly cutter). My mini mill if set to 100rpm would bog down and it would stop if I tried to drill a big hole. So I often set it to higher rpm, let's say 400, and during the cut I used the tool pressure to slow It down to my target rpm, for example 100rpm. This allowed me to use 1in drills in steel, bigger annular cutters etc. However, I never run 3in slitting saws on that mini mill so I don't know if this method is required or could you just set 100rpm and be fine. I do run much smaller slitting saws on my mini mill. For example a 1in diameter, 11 thou thick to cut screw slots.

I understand why you may prefer to run this speed, but I wouldn't recommend it to others.

 

[projectnut]

This may be a little late for your current project, but it's something to think about should you have problems finding the proper slitting saw for future projects. Several years ago, I was having problems finding the right thickness saws for a project. In my case the arbor is 1" and all the cutters with this diameter keyed hole were either unavailable or outrageously expensive. I could find them with 1 1/4", 1 1/2" and 2" holes for peanuts,

I ended up making adaptors so I could use the larger diameter saws on my mill. The adaptors consist of 3 main parts. First there's a spacer that has the inside diameter of the existing arbor and the outside diameter of the larger saw. It has an internal keyway to hold the spacer solid on the arbor and an external keyway to hold the saw in place. Then there are 2 end caps with internal keyways that also match the saw. Each end cap also has a setscrew in the end to position the saw in the center of the adaptor.

They can be made for any size arbor, and for nearly any size saw. Here are a few pictures of a few I made. The 1" keyed rod simulates the 1" arbor on the machine.