Dual jewler's saw horizontal mill setup to cut slot in square steel tubing?

gavingear · Mar 19, 2018

I've got a bunch of 3/4" .095" wall mild steel square tubing that I need to cut 3/8" wide slots in. I did some with a 3/8" endmill, and it was both painful and slow. So, I've been experimenting with various techniques to cut this tubing. I was thinking to go with CNC laser, but that proved (via two local quotes) to be cost prohibitive.

So now I'm looking at using a slitting saw (a thin jeweler's saw) to cut the slots- two small cuts to cut out a strip of metal. I did a quick test on my vertical mill, and I found the material to cut quite well, but it looks like power feed will be needed (I was hand cranking my mill on the x-axis).

This is the kind of quality cut I'm looking for, requiring only minimal de-burring:

And here's the setup I was using for the test:

After running this test, I'm thinking that this job should be done with a horizontal milling setup (with a horizontal mill, or a vertical mill with horizontal milling attachment) with flood coolant, and with dual jeweler's saws spaced appropriately to cut a total of a 3/8" slot in one pass. With power feed, seems like it would go really fast, and the jewleler's saws seem to cut great, esp. if I can get .001" - .002" per tooth feed rate. I do realize this is an exacting setup, and shattering the thin (.020" - .040" wide) saw blades is a very real possibility.

Does this sound like a reasonable way to do this job? I'm assuming the jeweler's saws will cut much more cleanly than a 3/8" wide horizontal milling cutter or saw... Any other ideas? Feedback would be most appreciated.

Thanks!

sfriedberg · Mar 19, 2018

You've found a setup that works, but if I had a bunch to do, I'd go with the 3/8" wide cutter. Probably a side-milling cutter, rather than a plain, for better clearance. If the 3/8" wide cutter is properly sharpened, it should be pretty clean on the sides. One swipe of a Shaviv or Vargus deburr tool on each side of the cut should clean up any residual burr.

The jeweler's saws cut tidy because they make little tiny chips, but they've got little tiny teeth which won't last in steel. The 3/8" wide cutter has robust teeth and can be resharpened.

gavingear · Mar 19, 2018

Thanks sfriedberg- are you thinking something like this HSS side milling cutter: 4" Diam x 3/8" Width of Cut, 24 Teeth, High 7314243 - MSC - MSC - 4" with 1" arbor. ?

sfriedberg · Mar 19, 2018

Yes, although MSC prices make me wince. Moon Cutter's 2014 catalog price was $75, about half of MSC's price. And Moon is the maker, not a distributor.

I also don't like the shape of the teeth in that MSC illustration. Looks more like a wood-working shaper cutter than a metalworking side milling cutter. However, online catalog illustrations are notoriously inaccurate, so who knows what MSC might ship you.

gavingear · Mar 19, 2018

Thanks, $75 would be doable!

Illinoyance · Mar 19, 2018

I am wondering if the .095 wall is stiff enough to take the 3/8" wide cutter. It might deflect too much under tooth pressure. I would be inclined to try two slitting saws on a single arbor. Should be doable on either a horizontal or vertical mill.

metalmagpie · Mar 21, 2018

If you are having trouble milling a slot, I suggest chain drilling to remove most of the material before milling.

metalmagpie

gavingear · Mar 21, 2018

Thanks for the suggestion, but that would be WAAAAAAAAAAAAAAAAAAAAAAYYYYYYYYYYYYYY to slow

With the slitting saw setup I believe I can do 48" in about 2-3 minutes total.

Greg Menke · Mar 21, 2018

I like slitting saws on the horizontal-that tube looks plenty stiff so there might not be a lot of benefit to putting the workpiece down on the table or otherwise supporting it. .I'd go for the thicker saws rather than thinner, smallest diameter you can reasonable use, gang tooled on a stub arbor- might have to make your own spacer to get the right distance between them.

.095 in a single pass is a pretty deep cut tho, a couple light passes (eg no more than .020 max) to establish a straight kerf is helpful. +1 on the flood coolant, it really helps keep the small teeth clear and sharp. Watch your cutter rpm tho, the thin saws can burn teeth very easily.

DOesn't look like its really appropriate for your setup, but if you can plunge then cut towards the end of the piece rather than from the end, it may help too; perhaps plunge and cut to the end for to make the slits, then a full-depth final pass in reverse from the end to define the endpoints of the slits.

If you're careful with your tooling and technique you can easily hold +/- .001 parallelism on the slot edges. Too great DOC or dull saws will tend to make the kerf wander to one side or another.

gavingear · Mar 21, 2018

Greg Menke said:
I like slitting saws on the horizontal-that tube looks plenty stiff so there might not be a lot of benefit to putting the workpiece down on the table or otherwise supporting it. .I'd go for the thicker saws rather than thinner, smallest diameter you can reasonable use, gang tooled on a stub arbor- might have to make your own spacer to get the right distance between them.

.095 in a single pass is a pretty deep cut tho, a couple light passes (eg no more than .020 max) to establish a straight kerf is helpful. +1 on the flood coolant, it really helps keep the small teeth clear and sharp. Watch your cutter rpm tho, the thin saws can burn teeth very easily.

DOesn't look like its really appropriate for your setup, but if you can plunge then cut towards the end of the piece rather than from the end, it may help too; perhaps plunge and cut to the end for to make the slits, then a full-depth final pass in reverse from the end to define the endpoints of the slits.

If you're careful with your tooling and technique you can easily hold +/- .001 parallelism on the slot edges. Too great DOC or dull saws will tend to make the kerf wander to one side or another.

Thanks Greg- what width saw would you reccomend, and assume 2" saw, what speed/feed would you expect (ballpark is fine). Appreciate the input!

Greg Menke · Mar 21, 2018

I like the .030" ish thickness but I mostly saw solids with it- minimal kerf kinds of ops. Sawing thru like you're doing I think thicker is better. The thinner the saw the more easily the kerf wanders and more prone to breakage. A thicker saw will tolerate more drama than the thin ones.

As far as feeds and speeds, I try to go right out of the tables, and less 10-20% from there. A production feed is preferable to a screw fed because you can more clearly feel the cut- its really easy to overload the saw. If you have a settable power feed instead of cranking-while-counting, then I'd start with a low-ish feed and work up while holding rpm. Might help to use a standard DOC eg .020, to get a baseline on how the setup works. If the saws are happy you can always hold rpm and feed and increase doc to save time since you're likely feeding with the knee.

L Vanice · Mar 21, 2018

Distortion has not been mentioned, so I will. Cold finished square tubing will distort when sawed or milled lengthwise. I could see the distortion in the second picture in post #1. Note the upper kerf width is wider at the left end of the slot, where the tube is free to expand. The kerf narrows to the width of the blade at the right end of the cut, where the uncut tube material is holding the edges of the cut together.

If the tube is held in a milling vise on a horizontal mill, two saw cuts or one cutter slot will maintain a straight line (slot width) while the tube is held in the vise. But the vise may try to close the slot as you get near the end of the cut at the far end of the jaws. Then, when removed from the vise, the tube will distort, opening the slot width and making the square cross section into a trapezoid. Maybe a rolling operation could get the tube square again.

Larry

gavingear · Mar 21, 2018

L Vanice said:
Distortion has not been mentioned, so I will. Cold finished square tubing will distort when sawed or milled lengthwise. I could see the distortion in the second picture in post #1. Note the upper kerf width is wider at the left end of the slot, where the tube is free to expand. The kerf narrows to the width of the blade at the right end of the cut, where the uncut tube material is holding the edges of the cut together.

If the tube is held in a milling vise on a horizontal mill, two saw cuts or one cutter slot will maintain a straight line (slot width) while the tube is held in the vise. But the vise may try to close the slot as you get near the end of the cut at the far end of the jaws. Then, when removed from the vise, the tube will distort, opening the slot width and making the square cross section into a trapezoid. Maybe a rolling operation could get the tube square again.

Larry

Good insights! I've milled about 36' of this with a 3/8" carbide endmill, and did get some distortion, but not nearly as much as I expected... A bit of a wild card depending on the lot of material, etc.

onecut · Mar 21, 2018

Vertically I would use a 3/8 coated 3flute slot drill plenty coolant dont know why you say it took too long power feed it thro on at least a 2.5ins feed and increase if your happy with the results.But the best way would be a stagger tooth side and face cutter on a horizontal mill one cut 2.5 feed hand feed from end untill its cutting on all teeth then bump feed up as you engage the power feed.Have about 1/4ins of the job sticking above the vise and beware of overightening and the material closing in on cutter as you cut but this is only caution and it shouldnt happen in this case.Sawing it bit long winded but if you insist 2x as thick saws as you can get away with stagger toothed and straddle mill both cuts at once/plenty coolant and dont like your set up balanced in fresh air with no end support.Not much you can do about the springing of the slot other than closing it after maching,or rough/straighted/finish but that takes time.You could even consider a stagger tooth "T" slot cutter but that set up if you stick with it needs changing no matter what tool you consider like said I would do it horizontally but if you stick with that set up vertically I would stick a knee plate on table with a jack under end tube.A small "G" clamp on the inside of the end of the tube and nip it to the knee plate and a clamp on the knee plate acting as a stop to stop it lifting

LKeithR · Mar 21, 2018

Before you give up on end mills I would try a roughing cutter. The interrupted nature of their cut should make a difference
in how fast you can cut and how much chatter you get...

Greg Menke · Mar 21, 2018

Good call on the distortion. It might be helpful to clamp the workpiece normally but rest the end being cut in a vise with light clamping pressure to constrain the material from expanding but not enough to compress the kerf. A drillpress or toolmaker's vise for instance, not itself fixed to the table.

(on edit)- really like the slot drills for this, a lot less fussy than slitting saws are likely to be if you're going for quantity.

gavingear · Mar 21, 2018

RE: way too slow- I was responding to the "chain drilling" comment (drill holes along the length - probably over 100 for 48"

RE: Slot drills - which type? I see this term used somewhat interchangeably with endmill. The endmill trials I performed were single pass (with end plunged down in middle of open area of square tube) with a solid carbide 4-flute endmill. Took a very slow feed rate - seemed WAY slower than the slitting saw test I did, and WAY more vibration and commotion.

Edit: And I was using cooling mist for both trials.

Illinoyance · Mar 21, 2018

Translation: Slot drill = 2 flute end mill on he other side of the Atlantic.

gavingear · Mar 21, 2018

Illinoyance said:
Translation: Slot drill = 2 flute end mill on he other side of the Atlantic.

Thank you! BTW: Why 2-flute slot drill rather than 4-flute?

L Vanice · Mar 21, 2018

gavingear said:
Thank you! BTW: Why 2-flute slot drill rather than 4-flute?

For clearing chips out of a deep slot in solid metal, a 2-flute end mill will be less likely to jam up than a 4-flute. Chip clearing in tubing will not be an issue, so four flutes will work OK.

I have USA-made 2-flute straight flute end mills that are one or two thousandths under a nominal size. They are designed for milling keyways in shafts with the expectation that the resulting slot will be exactly on the nominal dimension, like .375 inch, instead of the cutter dimension. I think they are what was originally meant by the name slot drill. Ordinary 2-flute or 4-flute end mills invariably produce a deep slot wider than the cutter diameter. On the other hand, 3-flute spiral flute end mills will generally mill a deep slot the size of the cutter. Woodruff cutters will produce an exact to size slot, whether cutting a square key slot or a Woodruff key slot.

Larry

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