Author Topic: Slitting saws  (Read 4564 times)

Offline Allen Smithee

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Slitting saws
« on: April 01, 2015, 10:28:40 AM »
A while back when I was making replacement balsa-knife collets as a training exercise I used a 0.4mm slitting saw for a deep cut for the first time, and I noted that the cut (about 20mm deep) had wandered off-axis. AT the time I assumed this was a fixturing problem, but since then I've found that the saw wanders no matter how stiff the fixture is. Is this a general issue? Am I doing something wrong? Is it because it's a "cheap" blade (arceuro)?

My approach so far has been to position the blade [in the mill] behind the job for a 5mm depth of cut and then move the table to walk the blade through the job in a "down-milling" direction, repeating until I had the required depth. Two alternatives occur to me but neither feels right (to me - but then my machining experience is limited so I'm happy to be told I'm wrong!):

1. Do the whole cut in one go rather than in 5mm "nibbles"

2. Position the saw on-axis and push it into the job rather than across it, only walking it backawrds and forwards to flatten the base of the cut at the end.

Any advice?

AS
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Offline gbritnell

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Re: Slitting saws
« Reply #1 on: April 01, 2015, 11:56:05 AM »
Hi Allen,
I sometimes have this problem when using really thin blades. Usually when the blade starts to get dull this happens. What I do is to make shallow witness cuts all around the part I'm making and then finally cut through. What thickness blade were you using?
gbritnell
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Offline Ian S C

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Re: Slitting saws
« Reply #2 on: April 01, 2015, 12:43:28 PM »
0.4 mm
Ian S C

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Re: Slitting saws
« Reply #3 on: April 01, 2015, 01:02:16 PM »
The one thing I've learned the hard way with slitting saws is that they don't like 'climb' so stick to 'conventional'.

Simon.
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Offline b.lindsey

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Re: Slitting saws
« Reply #4 on: April 01, 2015, 01:34:12 PM »
And always use a slow rpm too. Heat, particularly with thin saws can tend to warp them as well as dull them more quickly.

Bill

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Re: Slitting saws
« Reply #5 on: April 01, 2015, 04:07:49 PM »
I've never managed to get blades to run true. Either there's been a slight wobble or some run out. Others have said this is quite common for slitting saws. I've just ordered a new MT3 Arbor so it will be interesting to see if it runs any better than my old plain shank version.

Can we see your knife handles Allen?

Offline petertha

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Re: Slitting saws
« Reply #6 on: April 01, 2015, 07:30:03 PM »
Timely post. I'm just about to do some vertical finning on the top of circular aluminum head. They are ~0.045" wide & maybe 0.350" deep. Is it better to do this operation in progressive depth passes, or go full depth but slow feed? Assume I should use cutting fluid specific for aluminum or WD-40? Also, because the blade will be entering the head blank on the curve side (fins either side of center), do you think there will be a tendency for the blade to 'lift' as the bottom edge contacts first? Hopefully this is clear, if not Ill provide a picture

Offline mklotz

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Re: Slitting saws
« Reply #7 on: April 01, 2015, 07:42:26 PM »
I always "nibble" my way into slitting saw cuts working on the (unproven) theory that the initial tiny cut serves to stabilize the saw for the next cut.  FWIW, I've had little problem with saw wandering.
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Offline BaronJ

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Re: Slitting saws
« Reply #8 on: April 01, 2015, 09:37:27 PM »
I initially had these sort of problems until I made sure that the mill head was properly trammed.
Best Regards:  Baron.

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Offline MMan

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Re: Slitting saws
« Reply #9 on: April 01, 2015, 10:42:51 PM »
I do the same as Marv, also no problems.

Mman.

Offline gbritnell

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Re: Slitting saws
« Reply #10 on: April 01, 2015, 10:53:00 PM »
Peter,
Using a slitting saw is a trial and error or should I say trial and learning process. There are a couple of things that help the process. The first thing is to use a slitting saw that has a coarse tooth pitch. This allows room for the chips. The second thing you want to do is conventional cut. Start out by taking a reasonable depth of cut, you don't have to pick away at it. The problem with going too deep is the flutes might not have a chance to clear the chips and one of them might pin to either the cutter or the parent material. Run the spindle slower than you think it should be. This is totally a feel thing. If it seems like the saw is cutting well and there is little resistance on the crank handle then you can increase the feed a little. If it seems like there is some resistance then increase the rpm a little until the cut smooths out.
Let the first fin be your learning cut. If it goes well then you can increase the depth of cut.
This is the procedure I used when doing the heads for my radial engine. I ended up going to full depth on each pass.
I use a little cutting fluid for aluminum, it's made by Rapid Tap but others made for aluminum will work just as well. I don't flood the saw but brush away the chips with a wet brush as it's exiting the part. This knocks of the chips before they get dragged back into the slot.
Using a slitting saw it kind of like using a cut-off blade in the lathe. When it's done right it's a piece of cake but as I stated at the beginning just feel it out.
gbritnell
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Offline PStechPaul

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Re: Slitting saws
« Reply #11 on: April 02, 2015, 12:03:43 AM »
I haven't used slitting (or slotting) blades very much, and it looks like it may require an accurate Z-axis adjustment on the mill, or possibly a milling attachment for the lathe. This is what I did on the lathe:
 

 

 
My idea for a milling attachment for the lathe:
 

 
That might not be a true slitting or slotting saw because of the side cutting edges. It might be called a slot cutter. Here are the other blades and the mandrel I got at Cabin Fever last year:
 

 

 

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