Getting tear-out - need advice

Hey all,

I'm new to CNC and need some advice on ways to avoid or limit tear-out. I'm using a Chinese CNC6040 with a 1.5k spindle and two end-mill bits that came with the machine: 6mm and a 3mm to carve a couple of name plaques on a few scrap planks of softwood(I don't want to be using any expensive material yet as I'm a complete noob.)

On my first attempt, using the pocket toolpath in vcarve, I used offset and conventional. This came out reasonable well but left very noticeable tool marks on the base of the pocket and quite a bit of tear-out around the lettering. My second attempt, using raster and climb(upcut), came out much better. It had fewer tool marks and less tear-out - although it did leave a little more fuzz.

I expect a few problems like this when using softwood, but what advice would you give to help limit the tear-out. And what spindle speeds, feed rate and cut-depth would you recommend (the pocket is only 5mm deep. I used 3 passes with the last being 0.3mm.)

Cheers,
Rye

Hi,

Quote:

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Originally Posted by Rye

came out reasonable well but left very noticeable tool marks on the base of the pocket

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marks at the bottom are usually caused by misalignment of the spindle (not exactly perpendicular to the machine base).

Quote:

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Originally Posted by Rye

but what advice would you give to help limit the tear-out.

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If wood tears out the tool is usually just not sharp enough. Tools desinged to cut steel for examle are dull by design in comparison to tools made for wood or plastics. There are also large differences between cheap and high quality tools.

Christian

Hi mate,

Thanks for replying. As I said I'm new to all this and kind of in at the deep end. Trying to soak up as much info as possible. I'm guessing the tool marks may have been because my spoiler board was springing up a little in the middle. I've got that sorted now and they've pretty much cleared up(just very minor abrasions.)

I've ordered some new bits but, until they arrive, I'm just experimenting and trying to gain some confidence using the machine with bits that came with it. My biggest problem is trying to get my head around speed and feed rates. I was thinking if I can get those roughly right I'd be able to limit some of the problems above. That's why I thought I'd ask you guys if you have any tips or advice.

Thanks again,
Rye

Hello,
Just jumping in on this - I am at the exact same stage, I am using the end mill bit that came with the 3040 router I just got and am driving it around some soft pine at the moment.
It's all going OK but like you I am experimenting with feed rates etc.
I am getting very rough top edges in as much as it is not a nice clean cut - the internal walls of the cuts are really smooth but it leaves a burr most of the way around the top.
I have learnt that there are bits for down cutting and up cutting. I have no idea what I am using, I suspect I will just need to go and get a decent end mill cutter for wood. I am thinking that a 'down cutter' will work best for me in terns of having the clean top edge.
Does any of this sound familiar?
Kind regards
Richard

You could use a ramped profile with very shallow DOC to mark the slot to around 2mm depth prior to cutting it, a bit like using a marking knife in conventional woodwork to prevent torn surface edges on saw cuts.

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Originally Posted by magicniner

You could use a ramped profile with very shallow DOC to mark the slot to around 2mm depth prior to cutting it, a bit like using a marking knife in conventional woodwork to prevent torn surface edges on saw cuts.

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That does make sense though the software that I am currently using to generate gCode does not support that.
I will look in to CNCUSB as that allows some creation of code independently.
Here is a picture of the kind of thing I am experiencing:

Attachment 23534

I suspect that if I 'face off' the entire piece after this work then the problem will be removed but I am just wondering, should it be like this? Is it the wood? Is it the tool? Is it the feed rate or speed?

Kind regards
Richard

A downcut spiral is what you want to use.

Sometimes if I want a small chamfer around the pocket I do an engrave cut first with a V tool, this leaves a nice edge but I only use hardwood and that always leaves a better edge than pine anyway.
A straight flute cutter would be better than the one you use at the moment or as suggested a down spiral generally works best.
These cutters give me good results at great prices; https://www.toolstation.com/shop/Pow...er+Bits/sd2579

Hello and thank you for that - I have been looking around at tools trying to find a downcut one - so far I have only found down+up cot ones which I don't think is what I want.
Might you be able to point me in a suitable direction - perhaps to a recommended supplier?
Kind regards
Richard

Thank you for that - I shall head over there now.

I am only playing on the soft wood at present but I will take a look at the down spiral bit to see how that improves things.
Kind regards
Richard

I am currently looking at part no. RDM62760 from here: https://routercutter.co.uk/rdm62760

Given that I am looking for a spiral end mill down cutter with 6mm shank, it looks like that is the thing.

Am I close?

Kind regards

Richard

A few other candidates here http://www.trendproductsonline.co.uk...ters-850-c.asp . The negative aspect of downcut cutters is that because of the shaving being pushed down and having no easy escape route it can get a bit warm and make the motor work a bit harder.Not normally a problem with sharp cutters.

Thank you for that. It seems that the dimensions of those cutters must mostly be based on imperial measurements even though they are expressing in mm - would that be right?
I have heard that I should limit the plunge depth to 75% of the tool diameter. I plan to extract the shavings via vacuum - most probably hand held close to the bit. One aspect of what I want to do is to remove most of the inside of a small block of wood measuring roughly 200 x 80 x 40 mm - I guess I could use the down cut bit first for the extremity of this cut and use an up cut bit to remove the bulk where the surface tearing would be irrelevant. Is that kind of process common practice?
Kind regards
Richard

Perhaps you want a router bit for cutting wood and a milling cutter for cutting metal?

Big thank you for all your help.
Got the top down cutter, had a go with it today, amazing difference, its now doing exactly what I want it to do.
Attachment 23548
Nice clean edges from top to bottom, no tearing, all good.
Thanks again.

Kind regards
Richard

Good to see you got it sorted. I've not cut softwood for ages and, TBH, I'd forgot what bit I used when I did cut it successfully (these days I mostly cut hardwood.)
Any chance you posting the cutter you used for future reference. Thanks.

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Originally Posted by Rye

Good to see you got it sorted. I've not cut softwood for ages and, TBH, I'd forgot what bit I used when I did cut it successfully (these days I mostly cut hardwood.)
Any chance you posting the cutter you used for future reference. Thanks.

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Indeed - I got the following:

part no. RDM62760 from here: https://routercutter.co.uk/rdm62760

A downcut cutter will give you a clean top edge. I have found that they do not work well alone, however. Because they have a "down" spiral, they do not clear chips at all. In fact, they force the chips to the bottom of the pocket. This can so jam the cutter that it breaks. (Guess how I know). I have found that I get the best results if I do an initial pass about 0.02" (0.5mm) undersize with a conventional (up-cutting) cutter, then make a final pass to finished size with a down-cutting cutter.

The cheapest way to get a reasonable finish is to use a straight flute cutter - like this https://www.toolstation.com/router-b...mperial/p46293 I have some in my Odds n Sods cutters box - they're OK ish but good value for occaisional use.

I suspect experiences differ in this area and it also depends on exactly what you are cutting. I'm in the middle of cutting some small, intricate shapes from 5mm and 6mm "aviation-grade" ply. Close-grained softwood with multiple thin plies. I'm using a 2mm up-cut single-flute cutter and I get good results with virtually no whiskering on the top surface. I do use the same trick as I do when cutting steel on the same machine - the final pass is full-depth with a very small step-over and this takes off the burr/whiskers. Both Vectric and Fusion 360 CAM make this easy to do.

For pocketing in wood which tends to splinter more, I wonder if an up-cut tool for roughing followed by a down-cut for finishing would work? Not necessarily something to use in a commercial workshop but for one-off jobs at home, maybe? Or you pay a small fortune for compression cutters which combine down- and up-cut flutes in one cutter.

The cheap toolstation cutters were recommended to me by the late Hobnob. He always seemed to know what he was talking about. For my small woodwork I tend to use these https://www.aliexpress.com/item/3296...chweb201603_53

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Originally Posted by Neale

I do use the same trick as I do when cutting steel on the same machine - the final pass is full-depth with a very small step-over and this takes off the burr/whiskers. Both Vectric and Fusion 360 CAM make this easy to do.

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Another way to do this in simpler software is to lie about the size of your tool (keep replies clean please!). Tell the first cut that the tool diameter is .4mm larger than it really is and that will give you a .2mm thickness of material to remove with the final pass.

For my fellow Australians I've found Adam's Bits a good supplier of straight flute tools. https://www.endmill.com.au/

Kit