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Cutting stainless steel on a CNC router, advice please?
I’m about to sail some uncharted waters……
I’ve got not one, but TWO jobs requiring me to cut stainless steel letters. (It is a highly polished stainless 1,2mm thick. looks like a mirror. And no, acrylic mirror not acceptable. It HAS to be Stainless. I have to do them in-house, since in the entire Namibia there is not a single waterjet or laser capable of cutting metals.
I do have one connection (about 400kms away) with a plasma cutter, but I am scared of cutting such a upmarket job on a 12 x 3m plasma used by a shipbuilder 😮
Sooooo, back to me trusty ole router. It is an industrial grade machine – Teckcel Enduro, with a 7kw spindle motor and a gantry as strong as a railway bridge. I also have a couple of router bits that the manufacturer sent me from down under when I last ordered some odds and ends to service the routers. On the holders for the bits it says "stainless steel" (The bits are not made of stainless, so methinks it is for cutting the stuff)
Now, for feedrates. I was thinking a VERY slow cut at VERY low rpm and LOTS of alcohol mixed with oil misted on the bit to keep it cool. My spindle can go down to 6000 rpm, so that is what I’ll use. Cut straight through in 1 pass, but feed very slow. Maybe 3 to 5 mm per second. (The bit is a 3 flute 6mm). Chip loads will be tiny, but at least it wont melt like ally. I "think" that was the feedrates I once read on the internet, but now cannot seem to find the feed tables for stainless again)
What do you guys think? Anybody tried it before? Or am I daft for wanting to try this?
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8 Replies
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I know your resources are limited Gert but isn’t there an engineering firm with a cnc mill that you could get to machine them for you. You may think your machine is rigid but they aren’t designed for this sort of work. 6000 rpm is way above what you should be for cutting something like stainless & if that’s as slow as you can run the spindle it will also have very little torque. Plus not having a flood coolant system isn’t going to help either, mist coolant won’t remove anywhere near as much heat.
Having said that I have read of people cutting stainless on routers with good success, it’s not that thick which will help. If you have a small sample or an offcut bit of stainless then worth a try.
Just out of interest what you going to do with the letters once cut? You will need to watch because if you are going to weld locators on to the back then you could end up marking the face of the letters if it is highly polished. -
Yes, Martin, I hear you loud and clear. I have pretty much the same reservations as you have.
For starters, I would have liked 1500 rpm better than 6k….
The spindle produces peak torque from 6000 – 12000 rpm, and peak power from 12 – 24 000 rpm.(Effectively. There is a small – less than 10% – drop at peak rpm) Power being Torque x RPM, this means that torque drops off proportionate to speed above 12k rpm, and power drops off proportionate to rpm below 12k rpm.
The spindle is rated at 7,5kW continuous, and 9kW at 60% duty cycle.(12000 rpm) At 6000rpm I thus have 3.75kW continuous / 4,5 kW at 60% duty cycle available. Power / Torque is not an issue here.
Heat is the problem. I’m thinking of glueing the stainless to a sacrificial sheet of Komatex, and will assist the mist coolant with a handheld spray can – like you use for spraying insectisides.
The letters will be mounted on 5mm Black Perspex, with a 6mm contour showing. I will glue 10mm dia 10mm thick Perspex pieces on the back, and tap them with a 6mm tap to accept 6mm stainless thread rod as pegs. On the second job the stainless letters are use to face Perspex build up letters with halo illumination.
I have always used mirror Perspex for jobs like this, but these 2 jobs are both "C.I. Spec" – deviating from their stated methods / materials can cost us loosing a contract, or having to drive a 900km round trip to re-do.
…….And I am curious to see if it will work or not :lol1:
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I was going to suggest blasting it with air to help cool it but that will play havoc with the mist coolant so probably not a good idea. :lol1: :lol1:
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We do have 2 routers – The bigger 3000 x 2000mm machine (with the spindle as described above) is equipped with a vacuum hold down system thet bleeds through an mdf sacrificial sheet. So flood cooling is not an option.
The older 4x8ft Teckcel is equipped with a flood cooling system, (@ 100 litres of water per minute!) but it has a smaller 2,2kW Perske spindle. (The stainless sheets are 4x8ft, so bed size is not an issue)
Maybe I run it on that router. Praying the smaller spindle will have enough grunt at low rpm to cut the stainless.
I pride myself that I almost never break a router bit. I’m thinking that reputation may be in for a beating in the next couple of days!
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I think Stainless is definitely Waterjet, Plasma or Laser territory, I always farm it out.
( I get that it is not so easy to do from Namibia. )
However I would be interested to see how you do get on if you try it.
Keep us updated! 😉 -
Job done 😀
What I did was:
a) Cover the backside of the Stainless with application tape.
b) Glued the application tape side to a sacrificial sheet with Wurth Bond and Seal
c) Used a 4mm 3 flute cutter @ 6000rpm. Plunge at 1.5mm/sec, feed at (!!) 2mm per sec with the mist coolant delivering about 125ml of alcohol in 4 minutes. And kept spraying the contact point with a water bottle.
Early (about halfway through the 1st letter) the bit got red hot. From that point on I just kept spraying water just about non-stop. The first "incident" did damage 1 of the 3 cutting edges, but I just plunged 1.5mm deeper to keep a "clean" area of the flutes in contact with the stainless.
Towards the end (13 letters about 250mm high) the bit did dull a bit, so there was a continuous red glow at the contact point. But it still cut fine.
First job done, and no broken router bits!
For the next job I’m going to do things different. I’m going to use Komatex as a sacrificial, and back the stainless with vinyl rather than application tape. Then I am going to edge the 8mm Komatex with 25×25 alu angle, and seal it off. Then I’ll flood the entire surface with 5mm or so of water, and turn off the mist coolant. That means the bit will be cutting under water. Voila, perfect cooling!
In Afrikaans we have 2 relevant sayings: 1: ‘n Boer maak ‘n plan, and (2) Nood leer bid. Translated, it means (1) A Farmer (Afrikaner) makes a plan and (2) Crisis teaches one to pray 😀
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If your generating to much heat Gert have you thought about uping the feed rate? You can’t reduce the spindle speed but increasing the feed rate should help reduce heat generated.
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Hi, Martin,
I wasn’t about to experiment, keeping in mind I only have 2 stainless cutters!
The cutters were sent by the manufacturer of the router (and has the same brand name)
I came upon a printout of e-mailed instructions by the manufacturer. The feedrates etc were copied from that, with the only difference being they suggested 3mm per sec with a 6mm cutter. I was using 4mm, so dropped the suggested feed by a third as well.
On the next job, with better cooling, I’ll give it a shot to try higher feedrates. Either way, keeping the stainless sheet under, and the bit IN, cold water, may just be the magic bullet.
I they order these polished letters again, I’m going to laminate silver Anacoil on some 2mm alu and cut that.
They wont even notice the difference 😉
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