CNC rpm & feed

[Rewound]

somethings not quite right there. face operations should remove all of the top face of your stock. i reckon you have a geometry selected that you shouldnt for that toolpath. leaving it there potentially presents material to your next toolpath that it isnt expecting to be there. if its cutting into the middle of that stock expecting to cut at 7mm deep, with that extra material there that cut may be 8mm or more depending on how flat your stock is to start with.

yes I thought it was odd too, but I have found the correct setting

but here is where it gets frustrating, to cover the whole surface I need to select "Outer Loops" if I select "All Loops" it misses the middle bit out

 

[Rewound]

the following 'tapered holes' was from a CAM that I made from a 3d drawing in Fusion, the simulation works perfectly in Fusion, however it fails on the CNC Router by making the holes too big - and I can see from the toolpath on the CNC Router where it has gone wrong (my red pointers)

what could cause this error?

 

[Steve Mehrlich]

Looks weird, I'd guess theres an issue with the geometry selected for the hole. What tool path strategy did you choose?

 

[Rewound]

Looks weird, I'd guess theres an issue with the geometry selected for the hole. What tool path strategy did you choose?

Adaptive - (is that what you mean by a strategy)?

 

[Steve Mehrlich]

Yes there will be a more appropriate toolpath like bore or something more suited to holes. I'm not Infront of a pc at the moment to advise definite terminology but try a different type of tool path.

 

[Rewound]

If you are going to use a cnc router to level a warped disc (400mm dia)
would you just create a linear path that goes from side to side, or would you try and make a climb cut all the way around the edge before the linear passes and how much woud you come down with each pass 1mm? and is there a minimun pass on wood?

(i have run a hand plane over this just to take the high bit off)

 

[Chief Sawdust Maker]

I would draw a circle a couple of mm larger than the disk and use an area clearance toolpath to machine the disk
Depending on the software you have you may have an option to take liner passes along X or you may have an option for a spiral tool path starting on the outside and working into the centre
What size bit are you looking to use? as this will dictate what you min and max depth of cut should be along with the amount of step over per pass
Personally I would use either a carbide spoil board flattening cutter 1 1/4 dia with around .5mm depth of cut and around a 50% step over
Another option would be a 1/4 spiral down cut anything between .5mm and 6mm depth of cut and again around a 50% step over.
Depth of cut, spindle speed, cutting speed and stepover will all be dependent on your machine, your spindle, your cutters and how you are securing the disk.
Hope This Helps

 

[Rewound]

I would draw a circle a couple of mm larger than the disk and use an area clearance toolpath to machine the disk
Depending on the software you have you may have an option to take liner passes along X or you may have an option for a spiral tool path starting on the outside and working into the centre
What size bit are you looking to use? as this will dictate what you min and max depth of cut should be along with the amount of step over per pass
Personally I would use either a carbide spoil board flattening cutter 1 1/4 dia with around .5mm depth of cut and around a 50% step over
Another option would be a 1/4 spiral down cut anything between .5mm and 6mm depth of cut and again around a 50% step over.
Depth of cut, spindle speed, cutting speed and stepover will all be dependent on your machine, your spindle, your cutters and how you are securing the disk.
Hope This Helps

Thanks for that - I am very limited with the tooling for this machine (if I get going with and show that I can use it they will buy whatever I need)
so what I was going to use for this experiment was a 19mm bit like this

was going to use a 12mm step-over (cut 12mm every pass) and cut 1 mm off
Using Fusion and its setting it to 5000rpm with 500mm/min ?
This is all very experimental to me so any advice / pointers would be much appreciated.

 

[Rewound]

was going to do a climb cut around the edge first

and then do a Face cut

 

[Steve Mehrlich]

does your machine have the ability to adjust the feed during the cut? 19mm bit, 12mm step over at 1mm deep sounds fine. id be tempted to speed up the rpm say 10000 and start at 500mm/min although i reckon this would be a bit slow and infuriating to watch. if you can manually overide the feed up a bit til your comfortable id do that.
my little desktop machine ran a 25mm surfacing bit at 1500mm/min at 2mm depth in oak this weekend with no issue so if your machine is of the workshop variety it will chew through a couple of mm no problem.
you'll probably see a little tear out at the edges, try and run your toolpath parallel with with the grain of the wood.
id use the face operation in fusion, it will do half the work for you. if you model the disc to the finished height you want but make your stock a couple mm thicker you should be good..

 

[Steve Mehrlich]

below was last weekends mission repairing an antique chair for my father in law. i used an app, reality scan, to to create a 3d model of a similar intact pair of cherubs and then scaled it to hopefully fit the gap. about 8 hours of machining in oak.

 

[Rewound]

that's quite fantastic, have you got it all put together yet?


a couple of questions;
What happens at tool changes, do you get a chance to manualy zero the Z, or do you have to use tool height offsets (G43)

On long programs, can you stop the job anywhere then go back to that line number the following day?

I'm slowly but surely getting going with this. just flattened a warped board that will form the base for my next table, and made up 80 small crosses doing all the lap joints (20 at a time) n the CNC
Going to attempt a rose next - which will involve multiple tool changes

where is it good to get 3d images - I see there are plenty online free stuff, but never happy about downloading these things.
do they normally come as STL's ?

 

[meccarroll]

It seems that what started out as a feed and speeds question has evolved into a general CNC conversation. I have not been following this thread recently because no new threads have been put up but I am interested in the conversasions so could people start new threads so me and others know a new discussion has evolved...just asking as it's all interesting stuff?

 

[Steve Mehrlich]

apologies for the late response to this.

that's quite fantastic, have you got it all put together yet?


a couple of questions;
What happens at tool changes, do you get a chance to manualy zero the Z, or do you have to use tool height offsets (G43)

On long programs, can you stop the job anywhere then go back to that line number the following day?

I'm slowly but surely getting going with this. just flattened a warped board that will form the base for my next table, and made up 80 small crosses doing all the lap joints (20 at a time) n the CNC
Going to attempt a rose next - which will involve multiple tool changes

where is it good to get 3d images - I see there are plenty online free stuff, but never happy about downloading these things.
do they normally come as STL's ?

in answer to the above it didnt bloody fit!!! i didnt think to check that the size ratio between the missing cherubs was the same as the intact ones so whilst it fitted the space it looked weird. back to the drawing board, i suspect ill remake the entire rest in one piece.

i have a little touch off height sensor set to the bed of the cnc. ive written a little macro using maybe a g28.1 for location which it then probes and sets the height . accurate tool height is critical when your roughing pass is leaving 0.5mm for a ball nosed tooled to finish after. setting the height by feel or a bit of paper normally leads to disaster.

ive had a little success with stopping a program half way through and restarting but not enough success for me to be 100% confident in it.

stl's id normally get off the internet but yes some sites look more trustworthy than others. stl finder , cgl trader are normally okay.