cnc crashes when cutting 2D profiles in wood

[chrisobrien07]

Hi, this is my first post here so thanks in advance for your help

My set up details are follows
CNC machine: Ooznest Workbee. screw driven.
Makita router for a spindle (1/4 inch collet)

Bit : Melin Tool Carbide Square Nose End Mill,
2 Flutes,
75mm Overall Length,
6mm Cutting Diameter,
6mm Shank Diameter

stock : maple or sapele 690mm(7) Long 119mm(X) wide 25mm high(Z)

I am having trouble when cutting 2d profiles through the 25mm
The operation I am trying to carry out is a 2D profile cut through 25mm of stock.
when the bit gets to be about half way through (12mm out of 25) the vibration levels increase.
This then catches the workpiece pulling it out of its clamps and the rest is history....

I increased the clamping around the workbed but the same happened again....
I have attached a few images of the setup of the toolpath for reference
if anyone can help me solve this I would really appreciate it.
I will try send image of clamping set up and the machine

Thanks
Chris

[magicniner]

For such an issue video with sound would be the best data source.
Have you tried halving your depth of cut until you don't rip your work off it's clamps?
You should be able to stall your router and axes before your work comes away from it's clamps.
Regards,
Nick

[DaveL]

Hi,
I have a workbee but have not cut anything as big and 3D as that. Unfortunately the picture of the path I find unreadable, could you repost the path details as separate pictures?
Regards,

Dave

Sent from my Lenovo YT3-X50F using Tapatalk

[Voicecoil]

You might also find using a shorter cutter helps = less leverage on the spindle mount = everything's a bit more rigid.

[chrisobrien07]

thanks for the replies folks...

I have pdf'd the toolpath settings.. hopefully that helps their visibility.
Also two short videos of typical operation.
you can see the clamping from these two videos.

The makita runs from 10,000rpm at setting 1 ... to 30,000 rpm at setting 6

https://1drv.ms/f/s!AkB76_oAdtF_guh6jjgvQ9UHM5Atwg

I have not video at the moment of the 2D contour operation itself... these are just videos from recent pieces....
let me know what you think

[cropwell]

Couple of comments :-

That clamping looks a bit flimsy to me. Also it is a bit far out from the workpiece, so the downwards force from the wing nut looks about 25% of what you could get by having the effort (wing nut) nearer the load in this 3rd order lever clamp.

The bottom of the Z axis looks perilously close to the workpiece to me. Are you sure it isn't catching when you get to a deeper cut?

I also use double sided tape a lot to stop the workpiece shifting horizontally.

Cheers !

Rob-T

[magicniner]

Follow Rob's advice, all his observations are correct, he's being very gentle when he says your clamping looks a little flimsy, it ranks amongst the worst I've seen, don't muck about, get some metal clamps and use them properly.

You have a significant lack of rigidity for what you're trying to do, your roller ways combined with the low mass of your system are allowing the cutter to bounce around and move away from the work, because the deflection is greatest at the tip of the cutter the side of the cutter can engage the work avoided earlier, as your cut gets deeper the side of the cutter will grab the material avoided higher up the wall by earlier deflection.
Getting rid of the rollers running in channels and replacing them with good quality linear slides will give you some improvement but you may still come up short on mass and rigidity.

[chrisobrien07]

Folks,
thanks for the replies,
I have some redesign of the Machine to do I think....
.
Clamping:
Better clamps are needed I am thinking those Ive linked to below.
redesign of the bed is also needed ...I am thinking of installing Tracks link
below also.
this change combined with the use of double sided tape should help a lot.
.
Rigidity of existing machine:
Yesterday I went along each of the rollers on the X axis and adjusted the eccentric nuts on the rollers to tighten them, I did notice an improvement. I will complete this for the remaining rollers.
.
Linear slides:
To do this I need to redesign the machine... so this is a phase 2 change and I am not ready for that yet. Before I commit to linear slides, Id like to do some engineering analysis on designs to ensure the design is going to be good enough
.
0.5in spindle:
having a larger collet will help vibrations as far as the advice I've been given goes... the chinese spindles i have seen only have a 0.5in n a 2.5Kw spindle. this is whole lot bigger than the 700w router I am using... but it would also be heavier and would just add to problems with the current machine.
.
Bits:
I definitely need to cut up to 30mm depth 2d profiles through hardwoods. this is for guitars and necks... any advice on bits for such jobs would be appreciated.
.

Clamps:
https://www.amazon.co.uk/POWERTEC-71083-5-1-Hold-Down-Clamp/dp/B075K4CTYM/ref=sr_1_2?keywords=cnc+clamp+hold+down&qid=1556527810&s=gateway&sr=8-2
.
T-Tracks:
https://www.amazon.co.uk/POWERTEC-71372-Double-Cut-Universal-Predrilled/dp/B07FF29M4Y?ref_=bl_dp_s_web_4030454031

[magicniner]

.
0.5in spindle:
having a larger collet will help vibrations as far as the advice I've been given goes... the chinese spindles i have seen only have a 0.5in n a 2.5Kw spindle. this is whole lot bigger than the 700w router I am using... but it would also be heavier and would just add to problems with the current machine.

The only thing a larger spindle can do for you is add mass, there is no magic in spindle capacity itself which can reduce vibration, only mass and rigidity will do that.
You can experiment with added mass with your existing spindle, there will be a sweet spot for each set of cutting conditions but more mass will always give some improvement as it's inertia will resist cutter deflection.

Looking at your video again your spindle mounting system could be massively improved by adding a second identical mounting ring and having the two as far apart as possible, your current mounting arrangement has almost no triangulation and will be a point of flex in the system.

[cropwell]

Have a look on t'interweb for 'toggle clamps'. Ebay sell shitloads from China. Also have a look at this kit from Chronos - Soba M6 Clamping Kit 36 pc (Ref: 120710).

I will have a look at your spindle mounting and get back to the thread. I have significantly bolstered up my spindle mounting, but it just shows everything else wobbles in my Dicey machine. Is there such a thing as engineering viagra? (Just to stiffen everything up).

OK back again : Your spindle mount has a couple of threaded holes doing nothing (is this the same on the other side?) You could probably put in some triangulation there to clamp to the Z axis plate.

Rob-T

[Dave the woodworker]

May be I am a bit late on this one but a company called RatRig (https://www.ratrig.com/) do an update package for the WorkBee.