# odd offset when profiling



## flyforever (Jan 4, 2013)

I've attached a pic for clarity. I am cutting 3/8" mdf with a 3/16" chipbreaker at .050 depth of cuts. Normally, this translates into many passes. However, I find that somewhere between 1/3 and 1/2" down, the tool leaves a slight offset all around the piece. When I am nesting different shape pieces, the offset is seen on all the pieces, regardless of size or shape. Can anyone guess why?
I am using only rough cut profile with no finishing cut.
thanks
tony


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## Quillman (Aug 16, 2010)

Wear line or chipped carbide on the profile. 
Or your router is not registering on the same axis as you plunge.
Fixed base routers are worse at re-registration, what router?


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## flyforever (Jan 4, 2013)

It's a k2cnc. I follow your analysis of possible issues, but if it were a chipped tool, why only on one depth( same depth) when I am cutting the piece in 6 passes? Also, if I use a "finish" pass, I can remove the offset line. A chipped tool would not do that?
The second suggestion is a possibility. How would one test for this?
tony


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## Quillman (Aug 16, 2010)

Without observation I don't know.
Is the work moving on that final pass? Is the head moving?
All forces may be maxed if that is a full thickness cut.
A new cutter shows the same thing?


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## Check twice! (Feb 11, 2008)

I had similar issues on our machine,, we tried changing the bit ,, slowing the feed rate,, decreasing the cut,,, but could not loose it. My son and I decided it may be the rough cut program and we ignored it, as it cleared up on the finish cut.

There may be an answer but if you are getting your finish cut to work cleanly,,, why worry!

Just my opinion!


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## bgriggs (Nov 26, 2008)

Your bit is deflecting, as it cuts deeper there is more leverage on the tip.

Either make your router mount more rigid or just use a finish pass at full depth.

Bill


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## flyforever (Jan 4, 2013)

thank you all for great suggestions. Based on my observations/experience and your comments, I've decided to hit the pieces with a "finishing pass" for the time being. The possible issues are many, and I don't have time due to production pressures. What started this is the fact that, at times, the pieces come out without the offset. When this is so, the only variable, it seems, is the quality of mdf, given that the g code , the machine and the tool are the same. tony


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## flyforever (Jan 4, 2013)

Another thing I observed is that the end bit I am using has an odd shaped tip. Can it be that this tip interferes for the first few cuts? It's an Onsrud 60-106 compression bit.
Onsrud Router Bits, Onsrud Cutter CNC Router bits – 60-100SE
tony


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## 4DThinker (Feb 16, 2014)

Compression bit is probably the reason for the mid-board flaw. For the first half or so, all passes are pulling chips up and ejecting them. Once you reach mid point the top half of the bit is throwing chips down, keeping them from being ejected and forcing the bit to re-cut as well as be pushed outward by the accumulation of chips. Compression bits do fine on a single finish pass though as they can eject chips outward to the previous clearance made by earlier passes.


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## subtleaccents (Nov 5, 2011)

I have cut a lot of MDF on my machine. (1/4" to 3/4") Using a 3/16" Onsrud up cut spiral I take one pass at full depth on 5/8" material without issue. If necessary, I will take a finish pass of .020. I have yet to have the line show that you are experiencing unless there is a chip in the bit flute. Is your machine a light duty unit that prevents a full depth cut in one pass?


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## flyforever (Jan 4, 2013)

Yes, the machine is a light duty router. I had purchased it when I cut only balsa. Now I am forced to use mdf and the machine cannot handle full depth cuts, although I've never tried.
As to chip on the tool, why then does the line disappear if I do coarse cut first and then a .020 finish cut?
thanks
tony


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## bgriggs (Nov 26, 2008)

flyforever said:


> Yes, the machine is a light duty router. I had purchased it when I cut only balsa. Now I am forced to use mdf and the machine cannot handle full depth cuts, although I've never tried.
> As to chip on the tool, why then does the line disappear if I do coarse cut first and then a .020 finish cut?
> thanks
> tony


If the line disappears when you take a .020" finish cut then the line was definitely caused by deflection of the bit during the course (heavy) cut. The finish pass is also sometimes called a spring pass because the blade springs out under pressure to some extent. 

The only way to get smooth roughing passes is with a very rigid machine. Obviously your light weight machine is flexing under load. So just plan on doing a full depth finish pass at the end.

Bill


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## Gandalf64 (Nov 4, 2012)

I tend to find the shorter the length of tool sticking out the collet but with enough flute length to produce the part makes it a lot more rigid and reduces push off.
Also a spring pass is beneficial in most cases, first profile pass with finish tool and then a second pass ( spring pass ) usually cleans up most imperfections .


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