Slitting saw problem

[Prowe]

Hi to you all
I have in the past used slitting saws very successfully for removing material, both on the lathe and the vertical mill, mainly in brass but on occasions mild steel. Recently however, whilst slitting to remove excess material on a pair of loco crossheads I broke several teeth from three different slitting saws. This was in the lathe with the saws on stub arbours and the blades varied from 1” – 3” diameter, all around 0.020” thick. Both the carriage and vertical slide were locked but not the cross slide which was being used to provide the feed.
I feel I may possibly be running the saws at the incorrect speed, but I have been unable to find any information on what should be the correct speed, plenty of info on end mill speeds and surface speeds for turning but nothing on saw blades. Please can anyone advise on speeds or anything else that I could be doing wrong?

Thanks,
Phil

[Jo]

Hi Phil,

My recollections is that standard saw rates should be 40 to 50 ft per min, so you need to use the diameter of your slitting saw to calculate the correct speed. Chose a speed that is on the slower end for steel, faster for Brass.

As for feed rates that depends on the depth of cut. 1/2 to 1 1/2" is normal, the saw will tell you if it is unhappy.

Jo

[hat]

On the subject of speed I agree with Jo - the likely cause of a broken tooth or teeth is that they have become brittle due to running hot - do you use a coolant or are you cutting dry? There is no problem cutting dry on mild steel but dont overwork the tool

[Nigel Bennett]

I was cutting some 3mm mild steel with a 3" x 1/32" saw last night. I used about 80rpm, noticing that it felt a lot easier cutting when I applied some neat cutting oil. (I admit it - the machine saws a lot straighter than I can with a hacksaw....)

[houstonceng]

The cross-slide on a lathe is set at a very slight angle to the face of the spindle so that, when making a facing cut, the lathe creates a concave surface. Depending on the depth of cut and "strength" of material being cut there will be a sideways stress on a slitting saw driven by the lathe.

Usually, this is not sufficient to break the saw, but - - -

[steammadman]

I beleave you can read all the books you like , each one will give you a different
cutting speed for a slitting saw.You are advised to take into consideration the diameter of the saw, the thickness of the saw,the number of teeth on the saw, the type and hardness of the
material being cut, and of coarse whether or not you use "cutting" oil.
After you have found your calculater,then found your referance tables,done all the calculations,come up with all the fancy answers, you have forgotten what you were calculating.

I was tought in the good old days,was to start with a reasonably slow speed , a steady feed
and then adjust as required, a little experience will soon tell you if you are going either too slow or too fast.
I f your unsure try on a scrap end of the same material, looking at the cut material will tell you
what you are doing , right or wrong.
50 pus years ago when i was an apprentice if you had asked about speed and feed rates the whole shop would have fallen all over the place laughing, and you would have finnished up with a notice on your back "CHEIF NUMBER CRUNCHER", or something similar, which i must not post on here.

[hat]

Yes times have changed - I remember vividly wanting to solve a problem using pi - but my mentor thought that pi was something that he had for dinner! I was sent for a "long stand" for suggesting some new fangled idea " from that bloody college" He was a top man but could hardly read and write.
However we must remember that many of us involved in ME do not have the luxury of a seven year apprenticeship and experience on the job - so books and a little academia help to keep our hobby alive.
I could rub a bit of grit into the thread by offering to post the mathematics

[Prowe]

My thanks to you all for the responses to my problem, its good to see how generous people can be with their advice.
I tend to avoid using cutting fluid except on a finishing cut because of the mess and it can sometimes obscure what is going on, but will bear this in mind for the future.
However, I believe I have now found out what caused my problem in the first place, whereas I thought I was machining a piece of ordinary mild steel (from my stock/other people’s scrap), in fact I was working with something very much harder., precisely what I don’t know.
Having purchased some EN1A at Ally Pally last month, I now realise how easy this is to work with and whatever the other material is, it definitely is not free cutting.
Perhaps now I will take someone else’s advice and colour code my stock when I know what it is and treat everything else with suspicion no matter how cheap/free it may be.

Regards to all.

Phil

[Lurkio]

Hi Phil,

You may be aware of this.
Depends on many factors, but if you're slitting tricky stuff it's often worth dispensing with the arbour key (if you're using one that is). Rely on the clamping force of the fastener only - tightened up just enough to cope with the job. Feed gently by hand and the saw will spin rather than break when 'something has to give'. Not ideal but better than the alternative.
As Steammadman indicates earlier, you need to 'feel' your way on these jobs.

Lurkio.

[chris vine]

Hi Lurkio,

This is sound advice (leave the key out) as long as the arbour is running really true.

If it is held in the three jaw chuck it will probably make it more likely to break a thin slitting saw. This is because if the saw stops turning it will then be nipped into the work by the eccentric arbour and then shattered. Because it is not turning it has no chance to cut itself out of trouble.

Don't ask how I know this!!!!

Chris.

[Myford Matt]

Just to echo the above, Arrand deliberately make their slit saw arbors without a key. If it's right for them then it's probably the right way to go.

MM

[steammadman]

never used a key on a slitting saw arbour , NEVER NEEDED ONE ! ! !
not in lhe last 50 years anyhow