Aspire 3D Roughing-Onion Skin

[Chuck Keysor]

Hello Fellow Shopbotters:

Using Aspire 4.5, I am now starting to move beyond my 3D modeling into 3D carving. I have a series of questions, all concerning the same design.

I will be making a test cut of this part (see first attachment) from 2" thick blue Dow Styrofoam. The part is 19" across the base and 25" tall, and with the exception of the foot, most of the model is 1" thick with tapering and valleys as indicated.

I will post my questions one at a time to keep things easier for me to track.

Thanks in advance for your help, Chuck
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Question 1: Roughing-onion skin, makes no sense to me....

For simplicity sake, I made a .1" thick "Onion skin" and I used a "machining allowance" of .04".
Using a 1/2" end mill, set for a pass depth of .5", the onion skin that I got, was .5" thick. I was surprised because I had thought the onion skin would turn out to be .14" thick.

So I experimented, and found to my confusion that the onion skin changes in thickness based upon the pass depth, when my inexperienced logic tells me that it should be fixed at .14" (I hovered the mouse arrow over the 3D tool-path simulation to determine the thickness of the onion skin.)

Pass Depth ____Resulting Onionskin
.1" _______________.2"
.2" _______________.2"
.4" _______________.4"
.5" _______________.5"
1" _______________1"

Question, why doesn't the onionskin work the way I think it should? Shouldn't it be .14"? Shouldn't it be independent of the pass depth?

Thanks, Chuck

[Xray]

All around, better to use tabs than "onion skin", which by definition can be very imprecise.

[Chuck Keysor]

Hello Doug. One of my coming questions is about tabs in 3d tool paths. Chuck

[gc3]

Hello Doug. One of my coming questions is about tabs in 3d tool paths. Chuck

combination of 2d 2.5d toolpaths...sometimes you gotta trick software toolpaths by making material height greater than actual piece...

[Joe Porter]

I think "Onionskin" refers to the amount left in a Profile or final cutout pass. That is, if you have 1" material and set your z zero to the top and your profile pass is set to a final depth of .98", that will leave you with a .02" onionskin to remove by hand, etc. Like Gene says, this is a 2D operation. If you are cutting out a 3D model, the picture of the slider showing where the model is in the material is how far down your roughing and finishing tools will go and the part underneath will remain, making your model thicker than you had planned. And, this will hold your part in place, thus that will be your "Onionskin". If you decide that you don't want that extra thickness and you move your slider down to the bottom, your tool will cut to the bottom and essentially leave your part free to move. In this situation, you would want to add 3D tabs to hold your model in place and have to remove them by hand. I hope this helps...joe

[Chuck Keysor]

Thanks for your replies. I am feeling that I didn't properly convey my confusion. Maybe I should have inserted one of these emoticons.....:confused:

In a general sense, I am confused over the way 3d roughing does not clear out the material at the edge of the part being cut the way it seems as it should. The Aspire training videos lead one to believe that 3d roughing, when an offset has been established, carves down the sides of the part. One 3d video says: " Boundary Vector Offest to force the tool to come out and down past this vector we've got selected, so that the sides get machined, and we've cleared away plenty of material around the edge of the model to allow for the finishing.

I always TRY to understand what I am doing, and usually things eventually make sense to me. To resolve my failure to understand, I am now wondering if the 3d roughing actually even cares about the sides of the part being cut. Maybe Aspire is just worried about the top surfaces, and they have tossed the 3d roughing cuts of the sides into limbo, assuming that they will be cut by subsequent operations.

Is that even a possibility? Or is my attempt to rationalize what I don't understand, more confused than my original point of confusion? Sigh :(
Chuck

[ssflyer]

Chuck,

Try using an offset in the roughing toolpath of the radius of the bit you are using. Toolpaths are always generated from the center of the bit.

Other things to keep in mind - if you have almost vertical walls (and sometimes if you don't - I do it out of habit) is to add a zero height plane to the job - keeps the bit from falling off the world...

[jamesb]

Chuck,
I am not entirely sure what your issue is from the description but it may be worth contacting support@vectric.com and ideally sending in some images or the actual part your working on as that will probably help to convey the issue and allow them to provide some information.

Thanks,
James

[Chuck Keysor]

Thanks, in re-reading my original post, I probably provided too much detail, and missed some important details, a bad combination.
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I should have had the headline: 3D Roughing confusion.

I should have said that: I used an offset larger than the tool radius

I should have said: With my material set-up (shown in the attachment) and my .040" machining allowance, I expected that after roughing, the remaining base layer/onion skin would be .140" thick, but it is not.

I should have then presented my little table that shows how the remaining base layer/onion skin and said this is even more confusing.
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I'll let this sit for a while, and see if someone else reads what has been written here, who can sense my confusion here. If nothing appears, I will follow James' good suggestion and check with Vectric.

Thanks, Chuck

[sevendale]

Chuck, please keep me posted on your onion skin issue (for instance where does that name come from).
I just had a similar issue using Aspire to rough a male mold for a sink: it seemed straight forward that if the part was 5 1/4" and the "material" was 6" and I set the gap to 3/4" UNDER the material then there would be 3/4" left on the bottom to hold steady.
Then I tried to fill in the spot where the overflow leaked and all heck broke loose. Changing any parameter may or may not cause the part to move up or down in the material.
Point is I think you're dealing with an Aspire default that doesn't get any buttons on the dialog box and is beyond the scope of the help file.
I "fixed" my issue by error and trial but I'd have to start from scratch to do it again.
How do I get this thing to ding me when another post happens?............
Thanks.

[sevendale]

What tool? A screen shot of that may not help at all but I could look at it and scratch my head knowingly.
Reason I ask is I can't imagine why you'd use an offset larger than the tool....
It is foam you're cutting so it won't hurt.
Also the .04 offset applies to the part not to the floor, that is determined by the height parameters you set in your screenshot. And there appear to be vertical walls........I can't go back to look while I'm typing... (opens new window to see same thread) yeah vertical walls.
You can outline the model in the modeling tab, offset that line about a toolwidth or two, and pick it with the model when you apply the toolpath and yes your path should fall off the cliff edge of your part but no further than the depth set by your set-up .1" and go out to the line and no further.
Am I helping here, cuz I'm learning it too and I don't have Aspire in front of me.