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servant74
Fri 19 June 2009, 19:46
Since I don't have a router running, I have a friend that has a CNC router that was not working and helped him get it going a few days ago. But this was the first time I had used a CNC router.

I was routing using a 3/16 HSS straight bit in treated pine deck boards. Router at about 19000rpm.

Even with a new bit it tore out, and it got worse as time went on. We were using between 60IPS and 200ips on the router (as specified in the program). Even running Mach3 I slowed and speeded up the cutting speed from the Mach3 console and it didn't seem to make a difference.

Most of the cutting was in curves (outline of letters). Each board took about 15 to 20 minutes to cut and there were 10 to cut. But the problems started with the first board.

Suggestions as to what I did wrong?

TIA, ... Jack

Gerald D
Fri 19 June 2009, 21:26
A down-cutting spiral bit is normally the easy answer to the problem.

Or, cut in two passes, the first one very shallow.

Gerald D
Fri 19 June 2009, 21:44
If you could literally see the cut getting worse as the day progressed, that also points to a bad cutter. You sould be using nothing less than carbide cutters, preferably solid carbide (not welded on)

Richards
Sat 20 June 2009, 09:17
The direction of cut may be a factor. Conventional cutting cuts against the grain and tends to cause tearout. Climb cutting cuts with the grain and reduces tearout. However, climb cutting also lets the router pull itself along the cut, so, depending on how your machine is built, more flexing (reduced quality) may result with a climb cut.

Gerald D
Sat 20 June 2009, 11:15
There are 2 different types of tearout:

1. Fibres break out of the surface of the material, along the whole length of the cut. Most of what Mike & I said above covers this type of tearout.

2. Sharp points break off the job as the cutter/machine makes a sharp change of direction (the tips of a square part break off). Our stragtegy for avoiding this is to nearly always cut counter-clockwise around a part (conventional cut) - it makes more tearout of the first type, but that is easily cleaned with a sander. However, a sander cannot clean the second type.

servant74
Sat 20 June 2009, 11:55
Thank you all. My tearout was all along the length of the cut.

Learning to use a new tool is always interesting. New tools, new techniques.

Another minor question, it seemed like the tool started burning out 'earlier' than it should, indicating to me that it was getting hot, and apparently getting dull.
Later on you could 'smell' the burn.

Is my diagnosis probably correct?

What could I have done to keep from this burning and 'early life' dulling happening? (Assuming that is what it was.)

TIA, Jack

javeria
Sat 20 June 2009, 12:50
Jack - HSS wont work - carbide tools or atleast carbide tipped ones work!

HSS will dull out.

Gerald D
Sat 20 June 2009, 13:20
Also strongly suspect you have/had a cheapie HSS (high speed steel) cutter in there. They are not good enough for CNC cutting of wood.

servant74
Sat 20 June 2009, 14:03
I am just glad someone is letting me learn a bit on their machine! Hopefully I can pass along your guys education so my friend can learn too!

Kobus_Joubert
Sun 21 June 2009, 00:05
What about feed rate. If you cut too slowly the cutter will also BURN

servant74
Sun 21 June 2009, 06:40
I did think of that while there and varied the feed rate. In the program, my friend set it to 120 to 160 ipm, depending on (random event). But all the programs were mainly curves or short lines (outligning letters using the Comic font), so it seldom got up to those rates. Even when it did, I didn't see any significant difference, whether I slowed the rate eveen to 60 ipm, or up to 200 ipm.