Roughing vr finishing - be aware of roughing "stock to leave

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Roughing vr finishing - be aware of roughing "stock to leave

Postby larynx » Sun Oct 13, 2019 12:44 pm

Roughing "stock to leave"

Just thought I'd throw this in since I never quite understood this setting. But it is plainly clear [frequent users of MeshCAM most likely know this but new users may not].

Stock to leave will leave TOO MUCH stock for the finish operation to cut through if set too large for the purpose of fine finishing - especially in wood or metals. Simply put the finish operation DOES NOT TAKE UP OR BEGIN where the roughing operation ends. You, at least I, would assume if you leave "extra" stock in the roughing operation that the finish operation may take more than one pass to complete - it DOES NOT. If set too large, you will find your finish operation will ruin your piece, the bit, or something will break. Test it yourself. Below is an image of a "stock to leave" set at 0.20 inches and you can see the large gap between the rough and finish - wherein the finishing operation will be cutting chunks out of the piece if not set closer to what the bit can actually handle. Note the green is roughing, the yellow is of course the waterline and the checkered is the cut X-then-y operation - note the gap around the piece that the finish operation will need to hog out.

It would be nice to be able to set the roughing operation to leave greater amounts of stock, which means you could "rough" at greater bites, and then have the finsih operation set at smaller bites come along in multiple passes to finish. In wood, this may help prevent tearout. As it is, if you set the roughing operation to cut larger amounts of wood [roughing by definition] then you will perhaps tear out as it takes the last "large" cut pass before finishing - ruining the piece before it can even be finished. So it kinda means you may need to set your roughing to the same pass depth and overlaps as the finish, defeating the time saving. What it really alludes to is that if they use the same logarithm, then you may only need to run a roughing pass set at smaller "bites". Sorry long winded - but wanted to be clear.
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I am not aligned with nor do I have any relationship with MeshCAM or its staff other than being a user [that sounds a little like I have a dependency problem]
larynx
 
Posts: 92
Joined: Thu Oct 29, 2015 2:56 am
Location: East Central Florida

Re: Roughing vr finishing - be aware of roughing "stock to l

Postby larynx » Tue Oct 22, 2019 3:41 pm

So I thought I'd follow up - a few more details mainly for new users.

If you wish to rough or finish at different depths there is a way I have been using - you get the idea if you read the rest of the posts [one comes to mind from Randy]. Lets assume I wish to use a 0.750 bit for all passes. I Rough with the bit but set it as a 0.800 in my roughing pass, which leaves an additional 0.050 on the stock [with step-over and depth of cut set ot 0.060] but cuts the basic shape, then use the same bit set as a 0.775 [with step-over and depth of cut set at 0.030], and continue till I get where I want to be with the final bit cutting very little. Often the final "finish pass" is something along the order of only cutting 0.015 of the remaining stock. Very polished finish set with small step and depth of cut.

I use a few "exotic" woods and this helps me control tearout. Yes, can lead to longer machining times - but ONLY one rough pass with several finish passes slowly decreasing the aggressiveness of the cut on fibers that may tear. The finish passes do not take a long time cause they basically are one pass each - on the remaining stock, so it is acceptable for me now as things are. As to the "longer machine times - they are actually less on some pieces due to the very aggressive first roughing pass I can make which takes the longest time to complete [cutting some air too most of the time due to "pre-cut basic shapes". Yes, I load each operation separately, but you could "stitch" them together if you want.
I am not aligned with nor do I have any relationship with MeshCAM or its staff other than being a user [that sounds a little like I have a dependency problem]
larynx
 
Posts: 92
Joined: Thu Oct 29, 2015 2:56 am
Location: East Central Florida


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