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NPW_BESPOKE
14-01-2018, 07:05 PM
Good day

Sorry in advance if this is a thread that pops up regularly?! I'm fairly new to CNC and Forums for that matter (Hi!)

I'm running my first flat pack carcassing project in 18mm melamine faced chipboard on my machine soon and am just after a little advice....

I've got a 7.5kw spindle capable of running a top speed of 24000rpm
I'll be using an onsrud 1/2'' compression cutter.

I have done some test runs in material at general manufacturers guide line feed and speed rates with varying success - I understand there is always an element of trial and error but I always seem to get break out on the upper face of the melamine.

I now understand that the first portion of the cutter is up-cutting so that needs to plunge and cut past the top layer of melamine.

What I have no real idea of is how fewer passes I can get away with and perhaps this is ultimately why the compression cutter wasn't getting the results I require?

Can I cut 18mm in one?
Or is it best to do say 1 pass with an offset and then final pass cut profile to desired dimensions.

Sorry I know this is perhaps basic stuff to many.....I'm teaching myself as much as I can?!
I appreciate any help and give thanks in advance
cheers
Nick

Boyan Silyavski
14-01-2018, 09:25 PM
It will work in any way you use it, but it's really meant for 1 full cut into material. Its a trickier cutter to use and IMHO a finishing pass is needed for any hard part /melamine layer in that case/ whatever the cutter. I know that from cutting phenolic sheets with melamine layers both sides. It is very challenging to obtain a perfect not chipped edge.

Here is a discussion between people doing this all day which confirms what i say http://www.woodweb.com/cgi-bin/forums/cnc.pl?read=772857

NPW_BESPOKE
14-01-2018, 10:07 PM
It will work in any way you use it, but it's really meant for 1 full cut into material. Its a trickier cutter to use and IMHO a finishing pass is needed for any hard part /melamine layer in that case/ whatever the cutter. I know that from cutting phenolic sheets with melamine layers both sides. It very challenging to obtain a perfect not chipped edge.

Here is a discussion between people doing this all day which confirms what i say http://www.woodweb.com/cgi-bin/forums/cnc.pl?read=772857

Hi

Okay, cool - thanks for the advice and link. I'll trial cutter with one deep offset pass and then a 'through cut' with final pass.. the guys in the link mentioned doing final cut in reverse (conventional cut?) is this of great benefit to edge finish and reduce melamine chipping etc?

Ger21
15-01-2018, 01:36 AM
Whether you do it in one pass or two (onion skin) depends on the size of the part, and the quality of your vacuum hold down. (you do have a vacuum table, right?)

Do NOT climb cut, as it will leave a rougher edge. Conventional cut always with melamine (and most wood products).

Feedrate of 15-18m/min, and 16,000-18,000 rpm.

NPW_BESPOKE
15-01-2018, 09:00 PM
[QUOTE=Ger21;98845]Whether you do it in one pass or two (onion skin) depends on the size of the part, and the quality of your vacuum hold down. (you do have a vacuum table, right?)

Do NOT climb cut, as it will leave a rougher edge. Conventional cut always with melamine (and most wood products).

Gerry
Thanks for the reply. Invaluable knowledge and massively appreciate the advice.

Yes I do have a vacuum table (sorry cant find spec...) and am machining large parts (kitchen carcass panels). Had spindle speed about right but feed rate less than half what you are suggesting



one last question (sorry) regards cutting direction - will I gain anything (mainly cutter lifespan?) from running an initial offset 'climb' pass before doing final dimension profile as a conventional (melamine + most wood materials) ?

thanks again in advance

Nicko

Ger21
15-01-2018, 11:12 PM
Imo, no. Conventional cutting will give better tool life.
By doubling the feedrate, your tool life should also nearly double.

Ger21
15-01-2018, 11:23 PM
The reason that some people do a climb pass first, followed by conventional, is this.
At high chip loads like this, the cutting forces are pretty high, and with a conventional cut, will tend to pull the tool into the part, resulting in a slightly undersized cut.
This can also happen when onion skinning. The first pass will pull the tool into the material, but the final pass will be more accurate, and leave a small lip on the bottom of the part.
By doing a climb cut first, the tool is actually pushed away from the part, which leaves a small amount of material for the final, conventional cut.
But the climb cut won't cut as clean, especially as the tool starts to wear, so it may leave chips that won't be removed on the final pass.

NPW_BESPOKE
16-01-2018, 06:45 AM
The reason that some people do a climb pass first, followed by conventional, is this.
At high chip loads like this, the cutting forces are pretty high, and with a conventional cut, will tend to pull the tool into the part, resulting in a slightly undersized cut.
This can also happen when onion skinning. The first pass will pull the tool into the material, but the final pass will be more accurate, and leave a small lip on the bottom of the part.
By doing a climb cut first, the tool is actually pushed away from the part, which leaves a small amount of material for the final, conventional cut.
But the climb cut won't cut as clean, especially as the tool starts to wear, so it may leave chips that won't be removed on the final pass.

Thanks again Gerry
Great info - this I feel will become a major part of my machines work so much appreciate being pointed in the right direction...

Now to go and play...
Thanks again
Nicko

EddyCurrent
16-01-2018, 11:04 AM
One of the best methods to achieve a full depth cut is to use a trochoidal machining operation.
CamBam has an excellent plugin for such cuts if your current software does not.; http://www.atelier-des-fougeres.fr/Cambam/Aide/Plugins/TrochoPocket.html

Ger21
16-01-2018, 11:54 AM
There's no need for trochoidal toolpaths when cutting wood, and certainly not when cutting cabinet parts.