Stepcraft 840 not cutting to depth

Hi,

just some short comments from my side and hopefully other users have more ideas to help...

What spindle you are using? (Kress or...?)
What rpm?
What feed-rate in XYZ?
What CNC SW (UCCNC?

(1 = End Mill {9.53 mm}) :ohmy: Thats too much for a hobby machine I think.
I´m using 1-6mm in diameter with a 800W spindle (mostly not more that 3mm)

8mm per cut and a 9.53mm end mill...that totally out of range!
I´m very conservative I must say so with a 6mm end mill I would start with 0.5 - 1mm per cut and 800mm/min feed rate or lower.

What I think is that your machine is loosing steps since it is totally overloaded.

8 mm depth per pass on a Stepcraft! No way.

Yes, DocBrown is correct, crazy! I cut guitar stuff and my roughing passes are done at no more than 2 mm depth per pass. Take a look at this video in which I do a test cut using 5 mm end mills on the top side:

http://www.youtube.com/watch?v=1GlAxiVl2Mc

I had an electrical interference problem on the lower side using 6 mm end mills which caused a serious loss of Z steps but the spindle still ploughed on with probably 12 mm depth but I wouldn't recommend anything more than 2 or 3 mm and that's with a perfectly tuned Stepcraft and an industrial spindle.

You can find videos of test cuts on the guitar body sections here:

https://www.stepcraft-systems.com/en/forum/accessories/4125-industrial-quality-small-hf-spindle-from-stoneycnc

They were done using a 4 mm end mill with 1 mm depth per pass but 2 mm depth per pass will work. Also I go very conservative with Z plunge rates, no more than 120 mm/min. Treat the Steppi gently!

Doug

Thank you both very much. My friend who has the machine was the one who set the depth per pass... but I guess he's just as unfamiliar with it as I am! We ended up on a 1.25mm per pass depth and that seems to have resolved the issue.

If we were to go to a 1/4" 2-flue spiral up-cut bit for the control cavity (1.5" deep) and body profile (1.75" deep) would 1.25mm still be appropriate or do we need to step down a little (like to 1mm or less)?

Thank you both very much. My friend who has the machine was the one who set the depth per pass... but I guess he's just as unfamiliar with it as I am! We ended up on a 1.25mm per pass depth and that seems to have resolved the issue.

If we were to go to a 1/4" 2-flue spiral up-cut bit for the control cavity (1.5" deep) and body profile (1.75" deep) would 1.25mm still be appropriate or do we need to step down a little (like to 1mm or less)?

Hi CommandaZ

1.25 mm is absolutely fine. I didn't see which spindle you are using but I reckon 1.5 or even 2 mm will also be o.k. Best to simply set up a 'ploughing' toolpath to test on a scrap piece of timber to save ruining your stock. I did this and it paid off.

I started off using 4 flute bits for my timber cuts which generated very small chips (sawdust really) but was advised to use two flute bits on timber but you've already got that aspect covered. Don't vertical drill with end mills is the other tip. I blunted the 4 mm 4 flute flute end mill I used to cut the body sections shown in my videos by using it for drilling the dowel registration holes. It's difficult to believe that you can overheat and quickly blunt a solid tungsten carbide cutter bit just by doing some vertical drilling but I can confirm that it's possible. :ohmy:

Basically, the centre of the spinning bit is at zero velocity so end mills should always be run with a translation in the XY plane or else the bottom cutting face will overheat. It also compacts the spoil back down in the cut hole. You can work around this to some extent by using a smaller end mill than the hole diameter and describe an arc in the XY plane.

Doug

Awesome - thank you Doug. I don't have the machine at my home so getting the details will be a bit hard, but it sounds like we'll be alright. I appreciate you letting me know about the vertical drilling - I did have some concerns about that. I'll probably just buy a special drill bit for those purposes or something.