Hi All. Im a watchmaker using the Nomad Pro to make small watch parts. At the moment I am cutting watch hands out of CS95 carbon steel. The problem I’m facing is how quickly the quality of the finish degrades whilst machining multiple parts. The image below shows 3 hands that I have cut at once. The hand on the left is the first part to be machined and is beautifully sharp with minimal burrs/ imperfections and accurate dimensions. The other 2 hands have been cut afterwards.
The parts have been cut from 0.5mm CS95 steel that is spring hard. Im using a 0.7mm TiAlN coated carbide end mill. The steel sheet is 50 x 50mm and is superglued to a 6061 aluminium board that has been milled flat and checked with a dial test indicator for flatness. Once the steel sheet is superglued to the fixture I check for flatness again with the DTI. Each watch hand is 3mm by 10-15mm and takes approximately 10 mins to machine. All work is done using simple tool paths in carbide create. I run a pocket tool path for the holes and a contour tool path to cut out the hands. S&Fs are 0.05mm depth of cut, 75 mm/pm feedrate, 25mm/pm plunge, and spindle at 10k rpm. I use WD40 cutting fluid to aid the end mill, I usually do this by creating a dam out of putty around the parts, which gets filled with the cutting fluid.
It almost appears as if the end mill is wearing out after whilst cutting the first hand. Is there anything I can do to prolong the life of the end mill, and improve quality of subsequent cuts? I pay approx £10 per end mill, so that works out to £1 per minute in end mills!
I think the easiest solution would be to use a more machinable steel. CS95 is hardened spring steel. It’s going to eat cutters. Watch hands shouldn’t be subjected to any opposing force or wear, so hard spring steel isn’t necessary.
If it has to be CS95, consider finding someone with a laser or water jet, or invest in a laser head.
Thanks Tod, without a doubt that would be the easiest solution. There is no reason I specifically need to use cs95, I just need to use a carbon steel that I can harden and temper in the (home) workshop and that I can finish to a black polish. The reason I use CS95 is that it is the only steel I could find a supply of that met the criteria I need. If you have any ideas of alternatives I would really love to hear them.
Last year I actually looked for a company that could cut/machine these, but no one could or was willing to meet my requirements.
Assuming that making these on my nomad pro is my only option is there anything I can do to improve end mill life and quality of cut? Im sure I remember watching Winston machine tool steel on a nomad pro and mention tool life of at least a couple of hours (please correct me if I’m wrong). 10 minutes tool life seems ridiculously low.
If you have the capability to harden/temper, then you should also be able to anneal it.
Although it’s probably a lot more efficient to buy it pre-hardened, then just harden it after machining. (If you can find it.)
Will it be easier to machine in its annealed state? Im so used to machining Silver where you want it as hard as possible.
You’re exponentially making it harder (pun intended) by machining it in its hardened state. Specialty carbide cutters could be used to make it more bang for your buck but you’re going to be fighting a losing battle financially machining it in that state mostly due to rigidity. This rigidity can cause deflection which with other minor issues pile into chatter which is never great for cutters. Coatings can get you more life but TiAln is actually a bit of a special coating as it requires heat and force in order to perform it’s intended purpose. Coolant actually works against that and so you are actually working against it in a secondary factor. Personally I think TiAln just isn’t a very suitable coating for hobby grade machines.
If I were you I’d do several runs if you can afford it comparing with your coolant run and pushing your feeds and speeds to their limits as well just to see how much time you can get out of each cutter. If you plan on exclusively using these cutters for a long time it may be worth your while. Try it hardened vs annealed as well and see where you end up in terms of how long it lasts. Remember to keep your variables at a minimum so you’re only testing what you want to test.
Edit: I also see you’re using CC for this so you will want to make sure you’re using every trick you can to trochoidal mill, climb mill, ramp in, and avoid engaging 100% of your cutters diameter when possible. Climb milling usually when you want to put more heat into the tool would be minorly problematic but in the case of a hobby mill I’d guess it’s going to save you more tool life.
Thank you for all this brilliant information, I will run some experiments over the next couple of days. First one will be to try the steel in its annealed state.
Do you think I may see better results without the cutting fluid? I started using it because when I was engraving silver I got a much finer finish with less burrs, and just assumed it would also help with the steel.
Would setting up some sort of air blast also be preferable to using the cutting fluid? Could chip recutting be speeding up tool wear?
Sorry, for all the questions, last one for now - I currently use the free edition of carbide create. Is there a benefit to upgrading to pro? Will pro allow me to try trochoidal milling, climb milling, ramping etc?
silver is gummy in general even when hardened imo and is more likely to gall and embed itself and chipweld etc. Steel is more likely to just beat the everloving hell out of the cutter. What specific cutters are you using?
Airblast is very important for running AlTin as recutting of any kind is always bad. That without the cutting fluid should improve things quite a bit.
The way you are running coolant with AlTin is rough because in order for it to get up to temperature it needs a way to build heat and the coolant is taking all of that heat. So essentially what you’re left with is a cutter that is less sharp than an uncoated cutter and performing quite a bit worse which explains the 10 minute tool life.
No, in CC those are all done by using the software very creatively and analyzing your toolpaths, sometimes you have to trick it even to get it to work right and it’s almost never smooth. Best bet would be to slowly learn fusion while you hop along with CC for now. You will get things done but when it comes to steel etc you’re either going to learn alot of tricks to get CC to perform decently or learn fusion360. The downside to fusion 360 is they want 10% of your maximum allowable income on the free version as soon as you’ve made it so if you are running a watchmaking business and you’re recording your income well you know where that’s headed. The free version unfortunately doesn’t have rapids and each toolpath is its own program but, it will adaptively cut in ways that will save you alot of headaches and broken/dulling your tools faster than need be.
Thanks for this. I will try and rig some sort of airblast system for experiments - if they are successful I will invest in a proper setup. Im guessing from what you are saying about TiAlN that there would be no benefit of some sort of misting system to be setup with the arblast?
The End Mills I’m using are a generic 0.7mm square 2 flute carbide bit with the TiAlN coating. I will post a photo below.
Apologies for being slightly off topic but I am interested in your work holding of directly bonding the steel stock to machined flat Aluminium. I mill silver and getting a part to hold flat and true to stock in order to effectively use tiny bits to mill features is near impossible.
Questions on work holding technique:
- Does the super glue not soften and therefore loose work holding strength during milling?
- Do you use Acetone or some other solvent / technique to remove the part after milling without bending the part?
Thank you.
No problem Andy,
1/ Generally I find that super glue is rock solid. The only time it failed during machining was when I didn’t rough up both surfaces and clean them properly first.
I also machine sterling silver, fine silver, and argentium. One of the components I make with it is 0.2mm x 1mm x 6mm, and super glue is the only way to hold it reliably. It has never softened during use, even during prolonged sessions.
2/ I use acetone sometimes if the component is very delicate, but it can take some time to soften the bond. More often than not I use heat, applied with a small blowtorch until the glue fails.
Hope this helps.
That’s interesting. I will give it a try. Thank you for following up on my questions.
Hey after some experimenting in A36 I wanted to come back and say get 4 flute endmills for this, I had great success with just airblast on AlTin 1/4" endmill (the harder slicker brother of TiAln) at .0007 IPT at 12000 RPM 32ipm ran for 6 minutes and the wear seems very light. No coolant no mist still has AlTin on the cutting edges that weren’t already wrecked.
Given that this is around 700 SFM and steel desires far far less the tool wear should be much more but isn’t so who can complain.
https://deboertool.com/app/products/series/essential-series/categories/stub-length
These are 8.50 canadian per down to 1/32nd which is .09mm larger than what you’re currently using. Unfortunately the metrics only go down to 1mm
You were running a .0001 IPT I’d bump that up to .0005 and your IPM to 12 or about 312mm/m ramp entry should be 2 degrees I like to plunge at about feedrate/2.5
If you pick up the tool I reccomended change to 24IPM or 624mm/m
The depth of cut you could mess with but I was doing .003" you are doing .0197" and I suspect that might be part of your issue as we are only so rigid. I would half what you’re doing now as a starting point given that you have a more rigid machine than I.
These settings should give you about 100sfm which is a good starting point to try different options with.