slitting saw selection

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shorton

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I need to be able to make some small shaft couplers out of aluminum. To do so I'd planned to machine a ring out of 6061 1" alu but I need to add a slit to it. I've never used slitting saws and am not sure what to get. I have a small RongFU RF31 mill with limited speeds, and a R8 arbor, and a 6" Kurt vise.

I can determine the thickness (kerf) I need and I figure at my speeds I need to use HSS. But I'm pretty fuzzy on the diameter and number of teeth to choose, and rpm to run. I figure the cut will need to be no more than 1/2" deep.

Also advise on clamping and setup would be appreciated. I figure the way to do it is clamp it so it sticks out of the side of my 6" vice. If there's a more appropriate way, help appreciated.
 
I just did a .100-.125" slitting operation the other day making a 10-32 threaded collet to cut a shoulder on some set screws.

I chucked it just as you were thinking, hanging it about 40% off of my 6" drill vise in the mini mill. I have an auto feed which makes it really nice, but I just take it easy and take about .025" deep cuts at a medium-slow speed (I have a variable speed). You can tell by the sound, but his is not necessarily a high-RPM operation. So far, I've just used it for cutting aluminum.

I bought it from MSC about $25 per piece. I've used it several times now. You got to be careful though, this saw is extremely sharp! I just touched my fore finger setting it up and it draw blood.

IMG_0278.jpg

MSC:
Abor - ITEM #08271058

Saw-
ITEM #73312720

IMG_0278.jpg
 
If you're not real picky about the width of the slot, then pick up some blades from Harbor Freight. They have several different sizes designed for a small cutoff tool.
 
I'm happy to buy a quality tool, I was just hoping to choose the right one based on speeds, feeds, and tooth count.
 
I normally do small stuff like that with the same blades on my rotary tool mounted to the tool post.

Also they have the blades that are a bit bigger for the cutoff saw and others for the 4" table saw. You can also just use some of the small circular saw blades like the ones for small cordless circular saws.
 
I made an expanding mandrel the other day 2" od to hold a bronze bushing to turn the od of the bushing. I used a 2 1/2" saw not sure just how many teeth but looked about like a 10 pitch on a band saw blade it cut the full depth to the arbor in one cut just need oil, a steady feed slow rpm . I was on the high speed side as slow as my mill will go on a Bridgeport. I just wish I had a bigger diameter saw so if could slit it deeper so it would flex easier.

Todd
 
shorton said:
I'm happy to buy a quality tool, I was just hoping to choose the right one based on speeds, feeds, and tooth count.
Click to expand...

Actually the Horrible Fright HSS saw blades are quite good, you just don't have a lot of choices for thickness. GWizard shows RPM:707 and Feed: 33.5 IPM for the 1.75" 72 tooth blade assuming a .030 thickness and assuming I entered all of the parameters correctly :).
 
I've done a fair amount of slitting using my mill/drill, mostly in steel. I use a shop made MT3 arbor to hold the saw(picture below). The saws I chose have a 1" hole - this is a common size so I can get saws on eBay for modest cost. (Thurston makes good thin saws in the 0.010 to 0.040 range, sometimes available in lots of 5 for modest cost on eBay.) Slitting is a fairly slow process, at least as I do it - I've run into difficulties trying to go faster so for me slower winds up getting the job done quicker.

I prefer saws in the 2.5" to 3" diameter, thickness from 0.010" to 0.125". Thicker or larger diameter tend to stall or slip. I also prefer blades with coarse teeth, 28 to 36 in this diameter, because they're easily re-sharpened but thin saws generally have finer teeth so they get tossed when dull. My sharpener can't handle fine tooth blades. Blades often include a slot for a drive key which I don't use because I've read that if you advance too fast and the saw catches it breaks rather than slipping. I've had saws slip in the arbor and believe they would have broken had there been a key.

Blades under 1/16" thick generally are not side cutting. Blades from 1/16" up are optionally side cutting and I prefer these because they don't tend to wander off track and break. The non-side cutting blades need to be watched in use - best to make deep cuts using several passes no deeper than the tooth depth. Attempting to cut 1/2" deep in one pass may work but more often the blade will progressively walk off to the side and eventually snap.

Speed with this size blade should be low in steel, under 100 RPM. Aluminum can be run faster but be aware of heat from friction with the sides of the slot. Always use plenty of lube, cutting oil with steel or WD-40 with aluminum. The lube may cause the chips to stick in the tooth gullet rather than dropping free so I swipe downwards with a chip brush on the blade - opposite side from the slit, of course, to clear the chips and reduce friction. Add more lube as needed. Running at slow speed, blades last a very long time. Saws seldom run perfectly true so expect the droning sound to rise rise and fall in loudness with each revolution.

John




MillTooling2.jpg

MillTooling2.jpg
 
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