.014" slitting saw feed in SS

[Froneck]

I have to slit 82 slots each of 3 rows in SS schedule 40 pipe (actual wall thickness .100) Machine is K&T #2 (has speed selector on right side) Called saw maker and he recommended .003 to .005 FPT Speed 70 SFM. Cutter is 2-3/4 OD 72 tooth. He also said I could cut the full dept on 1/8". Didn't measure exact tooth dept but it's about 1/8" (I will get exact depth) I plan to start wit 1 saw then extend it to 8, maybe more later.
Does FPT = feet per tooth? So that .003 is .036"/tooth?
I've never cut with very thin blades, smallest ever was 1/16" wide in 4140 but only 3 pieces. Do the feeds and depth of cut seem correct?

 

[DavidScott]

Not according to Johnson where I got my carbide .025" slitting saws. I will finish this when I am at my computer.

Carbide or HSS?

 

[Froneck]

HSS

 

[DavidScott]

Sorry, I only have it for carbide. But here is what Johnson Carbide shows for their carbide slitting saws with your saw parameters in 304.

200 sfm 278 rpm
3 ipm @ .028 doc

It sounds really conservative doesn't it. I used a 1.5" diameter 32 tooth .025" thick saw on 416 SS and JC said to use the following for 1018, which is the free-est cutting steel they list.

350 sfm 891 rpm
5 ipm @ .028 doc

This was a production job so I ran the following with no issues and the tool wear looked appropriate for cutting 155 parts. This was cutting through a .312" wide section with a 1/8" hole in the middle to intersect another hole to the 4-40 screw could clamp the part onto a rod. I say this as how you feed the saw into the part makes a difference and the way I got to do it is the easiest on the saw. Once the saw was no longer making chips I fed it at 50 ipm until the saw was clear of the part. All very solid vise and saw holder on my Brother mill with flood coolant blasting the tool. The machinability rating for 1018 is around 70% and 416 is around 130%.

507 rpm 3.2 ipm @ .315" doc

While this doesn't help you much it does say I think your feed rate is quite high as well as the doc.

Here is a post that may be of interest but with a 1/16" thick saw.

https://www.practicalmachinist.com/forum/threads/slitting-saw-feeds-and-speeds-stainless.410295/

I am glad I'm not trying to do this job. Good luck!

 

[Conrad Hoffman]

What's the saw diameter? If the RPM has you much above 40-80 SFPM for stainless, expect short saw life. Excessive SFPM seems to be the most common problem with HSS slitting saws.

 

[Froneck]

As I mentioned above the cutter diameter is 2-3/4", width is .014", HSS. I purchased 2-3/8" OD bar stock to make spacers and support the cutter. I have 10 cutters, 32 are on back order but when I talked to the company they said they would rush the shipment to McMaster.
I received the information pasted below from McMaster when I asked for information

Please find the available information from the Saw Manufacturer (Malco) for the High-Speed Steel Slitting Saws (3062A35). For slitting stainless steel tubing, the milling speed would be 35-70 SFM for hard stainless steel and 70-105 SFM for free machining. The Corresponding feeds are .003-.005 FPT for hard stainless steel and free machining. You can review these recommendations on page 2 of the attachment.

Page 2 was a chart that gave speeds and feeds, can copy and paste here if requested.
Chart also included the Name of the company and a phone number. I call and was put in touch with Greg that knew quite a bit of what I was doing! When I asked him the depth of cut he said the full depth at the time I mentioned 1/8. I asked again the full 1/8" depth of cut is OK? He said yes!
Ah ha, I looked at the chart, it lists feed rate for 300 grade SS as .0003 to .0005 FPT! That changes the feed rate to .0036 Inch/tooth! But cutter speed listed is 400 to 850 SFPM. That don't make sense plus it states RPM = SFPM X 3.12 ÷ cutter diameter.

 

[DavidScott]

.0003-.0005" seems more in line from what I have seen, if not a little aggressive. Start slow, you can always speed up.

 

[Froneck]

I agree but speed seem very fast! The chart sent has the column hand written over erased original SFPM but it would make more sense if it were SIPM (I being inch) At 400SFPM sparks will fly and cutter destroyed in seconds! That's the slow end listed
up date:
I was wrong, noticed the attached speed/feed chart had 5 pages! Scrolled down to Milling Speeds and feeds. They were as listed by McMaster, 70-105SFPM and .003-.005FPT!
Another chart for saw cutting SS list cutter 2-3/4" 58 teeth as 150RPM Only 72 tooth cutter listed is 4"

 

[MCritchley]

Anything above like 30sfm is too fast.
Run oil, and the slowest feed the machine will run.
If the saw lasts increase your feed. Tubing is tough as it has two hard skins to cut through.

 

[Froneck]

If my memory is correct my mill's slowest fed rate is 1/4"/minute. Cutter tooth depth as best I can measure it is about 1/16". I can put it on my comparator to get exact depth. The chart does state oil is best lub/coolant for thin cutters.
At 30 SFPM thats about 42RPM X 72 teeth that is 3024 TPM. If only half of them cut that's 1512 TPN so at 1/4"/min that's .000165 per tooth. My concern is depth of cut, as i mentioned before the company said 1/8 depth of cut is OK, I think that is too much especially since the tooth depth is about 1/16"! Any thoughts on depth of cut?

 

[Conrad Hoffman]

I think the DOC is probably a bit heavy, but not much. It's OK for the saw to do some work. That said, I'd want flanges that support as much of the saw as possible, not some small arbor that lets the saw flex, which is a recipe for disaster, especially with a high DOC. Also, the thing better be concentric enough that more than half the teeth cut- that's just bad tooling or bad setup!

 

[Froneck]

I did mention I purchased 2-3/8" bar to cut into spacers so that the cutter will be supported. As far as 1/2 the teeth that was exaggerated worst case but even with new arbor and new cutters not all cutters cut the same depth due to concentricity issues. Of course I will do my best to get the cutters as concentric as possible! Saws have 1" bore so I must use a 1" Arbor, 8 cutters equally spaced in about 13.5" with run bushing at the end for support. Probably 2 cuts 1/16" per pass, probably lower the table for the return stroke. At this time I have 10 cutters waiting for back order to arrive.

 

[Froneck]

Up-Date I made the pipe holding fixture by milling a 1/2 round .50 radius slot in 7/8 thick X 17" long bar(customers supplied 17" long SS pipe that is supposed to be sch. 40 though wall thickness is .100"), OD varies but is about 1.040" One plate is mounted in pair of Chinese look alike Kurt vise that can be mounted sideways. My table is 12" so the two 6" vises fit. Clamped on the ends. Other jaw has 2 bars 8.50" mounted. .50 radius was cut in the bars when mounted in the vise so that .150" of pipe is exposed above the bar Clamp is solid and supports the entire 17" of pipe. Have a New 1" X 20" arbor that is just enough in length to allow 2" of travel. I made the spacers but taking time I only have 1 pair ground and keyed.
Wanting to test the cut, I mounted one .014" saw running at 47rpm and 1/2"/min feed (slowest feed rate on my mill). Made 3 cuts, first .040 deep to .140 total depth, then .060"and finally .070" in 2 cuts. I was surprised that the chips were very small, something like my cut-off band saw makes. Used Black High sulfur cutting oil.
So far so good! I'll keep adding cutters as I complete spacers. 20" long ardor was a bit short, had to make a 2" long run bushing, 3" long busing limited travel to only 1" I have a 26" long arbor on the way.

 

[Froneck]

More up-dates. I now have spacers made to stack 3 cutters. Had to make a number of spacers so I can move the stack since I only have about 2" of table travel available. Worked great! I have now 48 of the 80 slots in a row cut. Stacking 5 cutters in 8 groups, 40 cutters total a row can be cut in 2 moves. But I'm worried about the strength of my fixture. 40 cutters @ .014 = .56" of material removed. If the pipe turns that will ruin 40 cutters! The mill defiantly has the power to cut that but will my fixture be strong enough. I have a DoAll C4 cut-off band saw. Vise is not screw type, when I cut round I put a C-clamp on the jaws! If not round bar usually spins even with fine blade!
I'm cutting .070"/ pass, 2 passes for total .140" deep cutting time is slightly less than 10 minutes.
Maybe I should try 10 groups of 2 cutters.
Any thoughts on the issue?

 

[mattthemuppet]

if you're going to do a bunch of these it might be worth making clam shell type clamps specific to the pipe diameter that you can bolt directly to the mill table.

 

[Froneck]

As I stated earlier I have 2 vises that are a matched pair. I took a piece of 7/8" thick X 3.0" steel bar one cut 17" long (same length as the SS pipe) attached to both vises fixed jaws, other bar is 2 lengths 8.5" attached to movable jaws. I then took a 1" full round milling cutter and milled a 1" diameter slot .15" deep in the now attached vise jaws. Pipe averages 1.04" in diameter and used a 12" socket wrench to tighten the jaws as much as possible. I'm thinking that should be strong enough But if I'm wrong $990 worth of milling cutters will be junk!
BTW a .015" shim will not fit into the slot.

 

[Froneck]

I completed spacers so I have 10 groups of 2 cutters, 20 cutters total. I used the .070 depth that worked with 3 cutters. Knowing the pipe should have a seam I noticed a line on the inside of the pipe. There is no material increase anywhere that can be seen on the inside of the pipe so I used that line as the seam. Spaced the pipe with a line at 120° and insert the pipe in the fixture so line is at 270°. Took a cut with 20 cutters. 2nd row on the pipe I cut a row using 3 cutters. I then moved the table .388 (2 spaces 0f .194" center distance) Cutter near the middle of the pipe broke, cleared the area of any chips but then cutter next to it broke. I removed all the cutters, cleaned them and replaced the broken cutters. Reduced the cut depth to .035" cut again. Broke a cutter in the same location except 1 slot over.
Hard spot in the SS pipe? Any suggestions? I'm going to try undercutting the spacers. Cutter width at the teeth is .014" but at abut the bottom of the flute the cutter with is .013". My space diameter is 2-3/8", cutter diameter is 2-3/4" so if I undercut the spacer .005" on each side to diameter of 2.175" it will have a clamp width of .100 on the ends of the cutters.I'm using 47 rpm as cutter speed, could that be too slow? Feed rate is slowest I have at .5"/minute.

 

[DavidScott]

I'm using 47 rpm as cutter speed, could that be too slow?

Under magnification what do the cutter teeth tell you?

 

[Froneck]

All cutter teeth look good! The cutters that broke were new. To test the cut I started with one cutter and cut 10 slots. Then added 2 more cutters and completed the 80 slots in a row. Problem is travel. Being the length of the 80 slots is 15-5/16" and the pipe is 17" I only have about 2" of travel using a New Bison 20" arbor. Being the first cutter cut 10 slots then continued with 2 more cutters to complete the 80 slots it was the most use. When I converted to 20 cutters the mentioned 3 cutters were first on the arbor. and continued to cut without problem. Using 2 cutters in a group of 10 requires the table be moved 3 times @ .388"/move total of 1.164". (.388" = 2X center distance of .194")
Therefore one of the cutters cut about 30 slots and is still in great shape.

 

[steve-l]

The biggest issue when cutting anything is chip removal. There is no kerf with these saws for chip clearance, so chip bind is a large risk especially with such a thin saw. Secondly, 304 SS will wok harden, so it is important for the feed to allow cutting below the harder surface from the previous tooth. Lastly, 304, like 316, hates high surface speeds because tooth drag creates heat which creates surface hardening. That said, watch that the feed is fast enough so the chip is not so small that it wedges and jams, Once these parameters are met, adjust the DOC as to NOT overload the maximum torque the saw blade can handle. I return to my first point chip clearance risk, use compressed air if possible.