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Slitting Saws

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Graeme Barton29/09/2010 05:00:06
11 forum posts
Hi ,
thanks for the replys for my previous question about fly cutting.
Next up slitting saws?
How should these actually work? like a grinding disc or a milling cutter? i've tried every speed from about 60-300rpm on a 4" cutter and don't seem to achieve very much excpet creating a lot of heat. Is squirting cutting fluid enough or do i need to use a proper flowing coolant system. The blades teeth still appear sharp so doesn't appear to have done it much damage (ok i gave up pretty quick!)
As before any hints/tips much appreciated
Graeme 
Andrew Johnston29/09/2010 09:27:25
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7061 forum posts
719 photos
The slitting saw is a milling cutter. Calculate rpm, feeds and chip loads just like any other milling cutter. There are just more teeth to count! If things are getting hot that implies a lot of friction. Might be a feedrate problem. Feedrates for slitting saws are proportionally quite high, as there are a lot of teeth.
 
Don't bother with fine pitch slitting saws, unless you are doing a lot of shallow depth cuts such as slotting screw heads. The gullets clog up too easily.
 
Rules for coolant follow those for milling other materials, nothing special about slitting saws.
 
If the mounting arbor has a slot for a drive key, don't use one. If it all goes pear-shaped you want the cutter to slip on the arbor, not shatter.
 
My experience has been that on a stub mandrel on a vertical mill, there is a tendency for the slitting saw to wander off on cuts deeper than the few millimetres. On a big horizontal with outboard arbor support, no such problems.
 
Last but not least, whatever you do, and no matter how perfect everything is, the slitting saw will not cut evenly on all teeth. Don't worry about it.
 
Regards,
 
Andrew
KWIL29/09/2010 09:40:43
3681 forum posts
70 photos
If your saw in a stub mandrel on a vertical mill wanders off, there are two possible reasons, 1 the saw is worn one sided 2 the mill spindle is not truely vertical.
 
Graeme, is or perhaps it is , was your saw a new one or was it a reliable old make. There are a lot of useless products on our market from the far east, they may feel sharp but the teeth are all over the place angle wise and are often eccentric.
Ian S C29/09/2010 10:24:01
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7468 forum posts
230 photos
Graeme, could be worth looking to the thread on page 13(beginners), some useful tips there. I'v got two or three saws but don't often find a use for them, so I can't help much with expiriance. Ian S C
Andrew Johnston29/09/2010 11:25:17
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7061 forum posts
719 photos
Actually there's a third reason a slitting saw might wander off on a vertical mill. It might be due to slight deflection of the arbor. My vertical mill has a weedy R8 taper, while the horizontal mill is a rather chunkier INT40 taper. In practise I suspect that the wandering I've seen is a combination of all three factors. My saws are not new, although not of far eastern origin, and one can never get the mill trammed perfectly. As far as I recall the wandering was about 0.25 mm in a 25mm deep cut.
 
Regards,
 
Andrew
chris stephens29/09/2010 12:11:44
1049 forum posts
1 photos
Hi Graeme,
This might sound silly but are you sure you are running the saw blade in the right direction?
chriStephens 
KWIL29/09/2010 12:21:24
3681 forum posts
70 photos
What do you mean by a "weedy" R8 taper, there is no way a slitting saw could deflect a R8?
Tony Pratt 129/09/2010 17:27:58
2319 forum posts
13 photos
I agree with Kwil, from practical experience there is no way a slitting saw will deflect the bearings on an R8 taper. You don't state the thickness of the saw, depth of slot or work material but make sure the cutter is sharp, small cuts, slow feed and coolant is the order of the day.
If there is a lot of heat being generated you are running too fast, off the top of my head try 200rpm and don't force it through, take it gently!
 
Tony
Tony Pratt 129/09/2010 17:35:51
2319 forum posts
13 photos
Hi Graeme, bit hasty with my rpm suggestion, please ignore it until we know the material being cut.
 
Tony
Graeme Barton29/09/2010 18:01:45
11 forum posts
Hi there,
The metal is some 50x50 square black bar
The cutter is being held in an R8 arbour
The saw is about 2mm thick (can't remember the actual size, it's imperial) and was bought from Chronos 
Turning in the correct direction, maybe i'm not feeding it enough.
 
Not sure what Andrew Johnston is talking about? didn't know that the number of teeth made a difference. I was doing my very rough calculations on the diameter of the saw but if there's something else i should know............
 
Ta
Graeme 
Tony Pratt 129/09/2010 20:35:24
2319 forum posts
13 photos
Graeme,
4" diameter cutter cutting mild steel at 100 ft/min cutting speed would need to run at about 100rpm. Give it another go and report back.
 
Tony
Andrew Johnston29/09/2010 20:57:38
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7061 forum posts
719 photos
It's not a case of deflecting the spindle bearings. It's a case of the arbor deflecting. Unless you have an infinitely stiff arbor and/or zero cutting forces the arbor will deflect. Now I will admit that the deflection is very small, in order of a tenth or two of a thou according to my calculations. I expect in this case that it is negligible compared to the other effects. It was a slightly tongue in cheek comment.
 
Graeme,
 
Sorry I didn't explain myself clearly. As Tony says the cutter rpm is determined by the diameter of the cutter and the recommended surface cutting speed of the material. I agree with his figures. The feedrate is determined by the rpm AND the number of teeth. To take Tony's example of a cutter doing 100rpm. Suppose we want each tooth to cut about 2 thou of material. If the cutter has 4 teeth then the cutter will need to advance 8 thou per revolution. This gives a feed per minute of 0.008" times 100, ie, about 0.8"/minute. However, suppose our slitting saw has 40 teeth. Then the feed per revolution will need to be 80 thou for the same cut per tooth. This gives a feedrate of 0.08" times 100, about 8" per minute. The number of teeth doesn't affect the rpm of the cutter, but it does affect the feedrate.
 
I've added a picture of a slitting saw in action in my Odds 'n' Sods album.
 
Regards,
 
Andrew
Jeff Dayman29/09/2010 21:54:14
2356 forum posts
47 photos
Hi Graeme
 
In my experience if the saws are not good quality high speed steel they will have trouble with the hard scale on hot rolled (black) steel stock. You might try cutting some brass or leaded free cutting steel as a first trial of sawing. If these cut well, then your feed/speed settings and your kit are OK, you just got a bit of rough scaly black rolled steel.
 
I use my saws quite a lot, with good results, and they are worth the effort to figure out how to best use them.
 
JD
Bogstandard30/09/2010 03:28:57
263 forum posts
Just to add a litle to the discussion
 
 
 
Bogs
KWIL30/09/2010 09:51:23
3681 forum posts
70 photos
So it has depth control bumps like a chain saw.
Bogstandard30/09/2010 11:21:03
263 forum posts
Quite right Kwil, if you look at the last pic, you can see them.
 
That is why you have to make sure you don't feed too fast when used on something like a mill.
 
I'm not talking about super slow feeds, it did that cut in about 15 to 20 seconds, plenty fast enough for most people.
 
 
Bogs

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