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Slitting Saw - which one?

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ChrisB12/08/2019 16:21:40
648 forum posts
207 photos

I need help selecting the right slitting saw for the right material and the right machine.

I have a WM18 mill and want to cut slots 1mm wide in a hollow bolt with 7mm wall thickness. I'm not sure that the bolt material is but I will take it to be some type of high tensile stainless steel material. ( I'll try to find it's specs if its important)

I would like to know what type of slitting saw as in diameter, no of teeth, material etc I should use keeping in mind the type of machine I have (speed and feed limitations etc to prevent stalling the machine or burning the cutter)

Chris

Ron Olmstead12/08/2019 17:13:17
4 forum posts

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old mart12/08/2019 17:54:54
3345 forum posts
208 photos

You don't say what depth of cut is required, unless it is 7mm. Remember the cut will not be straight, it will be the diameter of the saw, so the ends of the cut will tail off to zero. The spindle speed will have to be very low, 100 rpm or less if possible, and the saw will have to be kept lubricated, tapping oil would do.

Arceurotrade have a good selection of arbors and saw blades.

not done it yet12/08/2019 18:09:05
6325 forum posts
20 photos

Doesn’t say more than ‘slots’. May be through from one side to the other, in which case the slot(s) could be cut across a diameter and so be flat at the bottom. Need a bit more detail?

old mart12/08/2019 18:36:52
3345 forum posts
208 photos

Dead right, ndiy, I was thinking lengthways.

One other thing, it is safer to leave out any keys that come with the arbor.

ChrisB12/08/2019 18:40:13
648 forum posts
207 photos

What I want to do is cut along the length, the whole depth i.e 7mm, but short of cutting the whole length. Sort of like a collet. I'll finish the end of the cut by drilling a hole. The material spec is SAE AMS 5935.

I'm not sure how well the WM18 can handle low speeds, it does have a low gear range. I would like some advice on what type of saw to get. The fixed parameter is the thickness of 1mm, but with regards to diameter, number of teeth or material I'm at a loss.

old mart12/08/2019 21:31:38
3345 forum posts
208 photos

The only way to get a square end to the slot, is to use a saw which has a radius large enough to reach the full length of the slot, not forgetting the radius of the mandrel. Drilling a cross hole where the end of the slot goes is a good idea and must be done first. If the slot is to be 2" long and the mandrel is 1 1/2" diameter, the saw diameter will have to be a minimum of 5 1/2" diameter.

pgk pgk12/08/2019 22:40:21
2317 forum posts
293 photos

Is it off the wall to suggest a 1mm dremel type cutting disc and bodge a mounting for the tool?

pgk

ChrisB13/08/2019 07:12:04
648 forum posts
207 photos
Posted by pgk pgk on 12/08/2019 22:40:21:

Is it off the wall to suggest a 1mm dremel type cutting disc and bodge a mounting for the tool?

pgk

If it were a thin walled say 1mm to 2mm that might work, but I doubt at 7mm...it will be very slow progress I think.

Old mart, I think I'll go for 22mm bore saw. Regarding teeth is there any recommendation, fine or coarse? On the Arceuro shop they have 80mm (max) 22mm bore saws. **LINK** The 1mm thick saw comes with 32 teeth, it is listed as fine teeth but I think it's not.

The 5" saw comes with 124 teeth but it's 1/16" thick, slightly more than I would like it to be, and the bore is 1". Would 124 teeth be fine? I've read on some other thread that too much teeth have a tendency to clog the wheel.

Chris

JasonB13/08/2019 07:18:07
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The smaller the saw diameter the faster you will be able to run it which will help with the risk of stalling but without knowing how far up the bolt you want the slot to go it is impossible to say what diameter. The other option would be to cut in from either side but that would leave a curved end to the hole not at right angles so could not be drilled.

Aim for two teeth in contact across the 7mm at any time, again this needs to be worked back from the diameter but avoid blades with too many teeth which you see a lot of people using on deep cuts.

No idea what the material machines like but looks like it may be heat treated and that could affect tooth wear and will give you the cutting speed which again needs to be worked back from the diameter of the cutter.

ChrisB13/08/2019 08:37:49
648 forum posts
207 photos

Thanks Jason, the bolt is 55mm in length by 40mm outer dia (26mm inside dia) with a flange at one end. I want to cut 6 slits 40mm down it's length.

I'll try to do some calculations and a drawing to see if I'm reasoning things the right way.

The material although tough is approachable by both a file and a hacksaw blade, so I think it's not hardened.

20190813_091634.jpg

PS. What's the O/D of the 1" arbour?

Edited By ChrisB on 13/08/2019 08:41:36

ChrisB13/08/2019 09:47:16
648 forum posts
207 photos

A 5'' saw will just pass by a whisker (if my estimate of 45mm od of the 1'' arbour is correct). On e-bay I have seen solid carbide saws if this does not work.

slitting saw.jpg

old mart13/08/2019 13:24:21
3345 forum posts
208 photos

The trouble with getting larger diameters of saws is the speed of rotation needs to drop. I would be worried about running an 80mm saw above 30rpm. As for solid carbide saws, they are expensive and very easy to break. Remember that to hold a saw with a 22mm bore requires an arbor of a greater diameter, so you loose cutting depth. There are lots of saws on ebay, some have greater tooth counts, which would be an advantage.

Thanks to ChrisB for the diagram, it makes understanding the problems much easier.

JasonB13/08/2019 13:26:06
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The R8 22mm ARC arbor that I have is 34mm OD so you will have a bit to play with.

For the 5" one you would want to be running at about 75rpm, definately use th elower speed range for the added grunt.

Ron Laden13/08/2019 14:17:57
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2248 forum posts
446 photos

I have 3 blades from ARC, a 1.0mm and 1.5mm x 80mm 32 teeth and a 3 inch x 1.8th inch 28 tooth. My experience with all 3 of them is that they work best at higher speeds than whats suggested, averaging them out I run them at about 50% more, I go steady with the feed though. Thats what I,ve found with them based on cutting mild steel but that will of course change with the type of material.

Clive Foster13/08/2019 15:49:46
2836 forum posts
103 photos

If you possibly can arrange for decent lubrication and some sort of positive chip evacuation. Slitting saws are one reason I put the SprayMist system on my Bridgeport. Minimum oil is enough to keep the saw lubed without fogging up the air too much and the air blast shifts the chips just fine. Feed rate needs to be enough to ensure the saw keeps cutting but not so much that chips crowd the gullet between teeth. At least the drilling provides somewhere for the chips to go in mid cut.

Job like that you can put money on locked up stresses in the hollow bolt wanting to come out and grab the saw. Lubrication gives it a chance to survive long enough for you to hear things have gone pear shape. I find that with a slitting saw sound is the best indicator that all is going well. And my hearing is poor.

Clive

ChrisB13/08/2019 15:54:39
648 forum posts
207 photos

I have found 100mm by 1mm thick 16mm bore HSS slitting saw locally at 15€. I'll try that out and see how it goes. As I'm not sure if it's going to work, rather than buying an arbour I'll make one, at least I wouldn't spend extra if I need to go a size up in the saw bore.

Thanks for all your help.

Will heed your advice John, lubrication is something I need to install at some point as well.

Edited By ChrisB on 13/08/2019 15:55:05

Edited By ChrisB on 13/08/2019 15:57:57

DC31k14/08/2019 07:05:48
573 forum posts
1 photos
Posted by ChrisB on 13/08/2019 09:47:16:

slitting saw.jpg

There is very little advantage and lots of disadvantages cutting it the way you show.

Right now, the teeth are cutting almost vertically. It might pay you to reduce the depth of cut so the lowest tooth on the saw just breaks through the wall of the tube. In this way, the teeth are cutting much closer to horizontally and the length of cut is at its maximum.

If you have some spare material, or similar material, turn up a close fitting plug for the bore and low-strength loctite it in. This will greatly increase the rigidity of the part and stop it flexing and trapping the saw as more cuts are put into it. Slitting saws do not like vibration. With the plug, and semi-horizontal cutting, you might be able to sneak a centre and tailstock support in. Even if not, support the outboard end with a jack.

Consider the pros and cons of conventional versus climb cutting here. Conventional will try to lift the part off the table, but you are always driving the work into the saw. Climb will push it down onto the table but the saw will try to self-feed.

Me, I'd grind the set off a hacksaw blade, sandwich it between two parallel guides and be done with it. Was it Sir Tubal or Uncle George who ground teeth in a feeler gauge to cut a very narrow slot?

JasonB14/08/2019 07:38:18
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You could actually do it with a 63mm saw on a 1" OD arbor and still be able to get your stress relief holes in if you cut each slot individually feeding along the bolts length.

bolt slot.jpg

ChrisB24/08/2019 15:55:59
648 forum posts
207 photos

Received three solid carbide slitting saws I bid on last week. A bargain for £15.

Made a 16mm arbor for the 63mm saw and tested the saw on the bolt I want to cut. Set the machine on low gear at 150rpm feeding slowly at roughly 0.25mm/sec with a 2mm depth of cut. All went well cutter cuts nicely and all teeth were still there after the test cuts.

videocapture_20190824-161506.jpg

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