What type of bit to use

Since starting the build of my CNC Router I've been unable to spend time researching what I will do with it once I've completed it owing to other projects. Well, that's about now, as all that is left is placing it on a 18mm ply sheet and connecting the spindle.

The main thing I wanted to do was cut shapes out of 4mm birch ply, but I don't know where to start looking for this information. Are there website that give this sort of info out, tables and list of the right bit for a certain piece of wood. The speed you should have the spindle set at and the speed of the spindle across the ply.

At present I'm using Inkscape and Cambam to get the Gcodes of what I want to cut, but Cambam asks a lot of questions I don't yet know the answer too so I'll have to read all the help files there.

If any one can shed some light on the right bits and the other things I'd be grateful to hear what you have to say.


Thanks a lot.

Your asking a question regarding speeds that is difficult to answer due to the very nature that each machine is differant. Some experimenting to suit your setup will be required. Often thou people go too slow rather than too fast and burn up cutters.

The type of cutter you'll most likely want to use will be spiral upcut to help clear chips. If breakout is a problem then you'll most likely want to use compression bit.

Please read this, i posted some pictures so you could identify the cutters http://www.mycncuk.com/threads/8326-Fine-detail-Wood


Basically even if the machine is not rigid- 16000 rpm, 60ipm, 2 flute, 1 diameter depth is a good starting point for routing wood. General rule is speed up until it breaks and then lower 5% the feed.
-best work straight 2-3 flute cutters and fishtail 2 flute upcut. down cut cutters IMO are not for hobby use or for people who start learning.
-generally at home you will use 3mm or 1/8" up to 6mm 1/4" , due to price, speed, material waste. So make sure you have all that collets.
-cutters smaller than 3mm need additional lowering of the feed like at least 1/3rd, same with long cutters
-hard woods need additional feed speeding to 17.000 rpm or even to 18000rpm
-more than 18000rpm is not a good idea as it wastes speed bearings unnecessary fast.

-cheap Chinese cutters break 5 times more easily than brand ones
-sharp brand cutters last 20 times more than Chinese cutters /micro grain carbide/
-Drillman1 at ebay sells best cutters for price for wood and plastic , Kyocera brand

Hope that helps:encouragement:

Thanks for your input lads,
Its a mine field out there. I thought I had my work cut out with Cambam, but the different types cutter seems even harder.

You'd think some one would right a book for us newbies so we could get our heads round this new fangled hobby.

I thought building the machine was going to be the hard part, but its the other way round.

I agree with you Silyyavski, a 2 flute cutter at 1/8 to a 1/4 would be a good starting point, but I've never been told to run something until it breaks and then decrease it by 5% until it doesn't.

What happens when the bit snaps. Does it fly out in all directions. Are there any precautions I should take when attempting this undesirable act.

I'll have a go at that and let you know the outcome.

Thanks again.

Michael.

Quote:

---

Originally Posted by centurian

I agree with you Silyyavski, a 2 flute cutter at 1/8 to a 1/4 would be a good starting point, but I've never been told to run something until it breaks and then decrease it by 5% until it doesn't.

---

No you won't be and shouldn't be told that because it's foolish and expensive way to go about learning.!! . . But don't worry about bits breaking they often just snap off and embed them selfs in the work or ping to the side. They don't shatter in all directions.

So many factors come into play but if you buy quality cutters from decent supplier they will offer you cutting parameters that you can use as base line. Then tweak to suit your machine.
If Machine is ridged then go with whats recommended but in general you may want to take whats recommended and Back off 30% to get a feel for how machine handles it. Then go up or down from there. This way you'll quickly find what your machine can cope with and not cost you fortune in snapped cutters.

Don't do what lots of people do and buy cheap cutters thinking it's ok for learning because it doesn't always make for good or enjoyable learning and can give a false reading of what the machine is really cpable off handling.
Quality cutters are completely different animal and can be pushed much harder than most realise, often harder than the machine can even handle.

You'll notice I'm not offering or recommending any feeds or speeds and for good reason.!! . . . For all I know You could have a chinese 3020 with Dc spindle that struggles to cut butter without burning up.? . . . . I don't know your machine strength, spindle power or the quality of cutter or grade of material etc. So dishing out cutting advise premerturely is pointless and potentially dangerous to your machine and wallet if not up to the task.

Buy decent cutters and use manufacturer cutting guide lines with good dose of common sense based on your knowledge of the machine and you shouldn't have too much trouble finding what can and can't be run at.
Yes you'll maybe break a cutter or two but you'll have fun doing it.!!

Its not necessary to break the bit, its more relatively speaking, though it could happen. Normally the bits are much more stronger than they look. What i am talking is when the feed is raised there is a moment where the cut quality starts to suffer and definitely it starts to seem like the bit will break. Usually it will not break. then back off a bit. The idea is for the bit to cut as its meant to cut, not just burn, like Dean said above.

The speeds i am referring will work on any machine , weak or not. At least on anything that could hold 6mm bit.

Manufacturers guides usually refer to industrial machines, so care should be taken making conclusions reading them. Not that they are wrong, we just have to start with much smaller depth of cut.

Basically that's the main trick. The speeds i was referring are perfect finish speeds. i will just change depth of cut depending on which machine i am working. people oftem mistake speeding with bettering the cut

OK then
It seems to be a case of 'Trial and Error' when starting out until you can find that common ground your happy with.

The machine is an OX from Openbuilds and the spindle is a Makita ( RT0700C ) No load speed 10,000-30,000 rpm.

Could you recommend a good supplier of decent cutters here in the UK as my local supplier sells Silverline which is cheap stuff. I want to start cutting with something half decent if I'm to get off to a good start.

Thanks to you both for your help.

Michael
Centurian.

Quote:

---

Originally Posted by centurian

Could you recommend a good supplier of decent cutters here in the UK as my local supplier sells Silverline which is cheap stuff. I want to start cutting with something half decent if I'm to get off to a good start.

Michael
Centurian.

---

I have found this firm very good. http://www.cutwel.co.uk/milling/milling-cutters
..Clive

Similar to my belt driven machine which is also with V bearings.

Then what i will say is even more true:Use 3mm and 6mm cutters, diameter depth at the speeds i indicated above. Bigger than 6mm cutter for surfacing needs to be making much more shallow cut. Same speeds and feed , 1mm usuall to 2mm max depth of cut and max 20mm cutter

and dont try to do aluminum