Separate Last Pass for reducing tool marks

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Separate Last Pass for reducing tool marks

Postby laflippin » Sat Apr 06, 2019 10:03 pm

Hi Folks,
I've lately been making some small oval boxes (4" x 7") that are anywhere from 1.5" to 1.8" thick. Some of these boxes have been cut from a single piece of Douglas fir and others have been cut from homemade laminates containing Doug fir, yellowheart, walnut, purpleheart and others.

Using a 1/2" end mill with 2" of cutting depth, it is easy enough to make these boxes with a pocket cut, followed by a profile cut (using tabs). However, perhaps not too surprisingly, both the pocket cuts and especially the profile cuts are leaving vertical tool marks that need plenty of sanding to remove.

I found a brief discussion of the "Do a Separate Last Pass" function in a Vectric tutorial about Profile Toolpaths. In the tutorial it was just briefly mentioned that the Separate Last Pass function may help to reduce unwanted tool marks and the suggested Last Pass value was just 0.01" (without further explanation, or any kind of demo of an outcome).

So, I tried using this function in a profile cut and used a Last Pass value of 0.02"--I figured doubling the suggested value might be reasonable given the rather large tool marks I was seeing on my boxes. Well, that didn't seem to make any difference at all! I'm afraid I wasn't paying close enough attention at the crucial time but...I'm not even sure there was a "separate last pass" in the actual profile cut. At least, the result didn't look any different than previous examples and, so, back to one of my least favorite woodworking activities.....more sanding.

I am wondering (1) if experienced users here at the forum might be able to help me out with their experiences using the "Do a Separate Last Pass" function within the Profile Toolpath menu; i.e., what values do you use and how effective are they? (2) I was also wondering if there is any help for reducing tool marks in the deep pocket cuts I've been making. There doesn't seem to be a corresponding "Separate Last Pass" option for pocket cuts.

Thanks in advance!
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Re: Separate Last Pass for reducing tool marks

Postby martin54 » Sat Apr 06, 2019 11:05 pm

Is it tool marks where the bit plunges you are getting? if so them you might look at using leads which can help prevent this so I have read, no experience with leads or the last pass feature personally.
What bits are you using? I often find straight fluted bits leave a better finish than spiral bits on certain types of wood :lol: :lol:
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Re: Separate Last Pass for reducing tool marks

Postby laflippin » Sat Apr 06, 2019 11:27 pm

Thanks, Martin! The tool marks are straight vertical lines where the bit plunges--especially bad where the tabs begin and end. The bit I've been using is a straight-fluted end mill, dia = 1/2".

If there is no really satisfactory answer for this issue I think maybe I'm looking at purchasing a decent table-top belt sander...maybe I should do that anyway. :|
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Re: Separate Last Pass for reducing tool marks

Postby 4DThinker » Sun Apr 07, 2019 12:48 am

Just like Martin, I'm going to recommend you look up lead-ins/outs to avoid tool marks from plunging/retracking.

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Re: Separate Last Pass for reducing tool marks

Postby laflippin » Sun Apr 07, 2019 3:20 pm

Thanks, 4D. Do you have personal experience using lead-ins/lead-outs to reduce tool marks in Profile and/or Pocket cuts? I'll look around for information on the lead-in function but would also appreciate anyone else who wants to jump in and shorten the trail on this topic.
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Re: Separate Last Pass for reducing tool marks

Postby 4DThinker » Sun Apr 07, 2019 5:56 pm

When I'm cutting the perimeter of anything I always use lead-ins/outs. When I'm using anything larger than a 3/16" spiral upcut bit I also use ramping for the initial plunging of each pass.

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Re: Separate Last Pass for reducing tool marks

Postby wb9tpg » Sun Apr 07, 2019 6:04 pm

I did my own separate last pass toolpath using an offset to control the amount it cuts. It uses the same vector as pocket toolpath. My pockets are 0.59" deep and cut with multiple passes and the pocket cut is run first (conventional cut). Then the profile tool path is run next at the full depth in one pass with a 0.02" offset (climb cut). I wanted to fully control the cuts myself.

BTW: If you make lids for your boxes offset is your friend as you can control the fit of the lid to the base.
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Re: Separate Last Pass for reducing tool marks

Postby laflippin » Sun Apr 07, 2019 8:09 pm

Thanks wb9tbg,

Yes, I do make lids for them and I typically do use a small offset so that the lids fit snugly, but not overly tight.
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Re: Separate Last Pass for reducing tool marks

Postby TReischl » Mon Apr 08, 2019 4:47 pm

A finish pass is the key.

If you are making tabs then lead in/out is only going to help at the start of the cut, it won't do a thing for those pesky tab tool marks.

I would not use a .02 "finish" pass. Typically I use somewhere between .005 and .010. Those marks are not as deep as they appear. On vertical walls I always use a Ramp tool path with Spiral checked. The problem is doing this with tabs. The tabs may not be strong enough to hold the piece while doing a finish cut. You will have to experiment with tab thickness to get a feel for what works. These days I am leaving tabs about .187 thick and it seems to work.

For finishing the bottom of pockets I use a .005 DOC and I set the step over to about 25% of the diameter.

For really nice work figure you are going to take a finish pass on every surface. I suppose that is why they call it a "finish" pass?

For some odd reason many of us seem to think that we should be able to take one pass on something and have a beautiful finished piece. Strange because as woodworkers we already know that surfaces require some kind of finishing after machining, usually sanding.
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Re: Separate Last Pass for reducing tool marks

Postby Xxray » Mon Apr 08, 2019 7:08 pm

Is "separate last pass" a function of the newest aspire ? I have never heard of it. If you are just doing 1 roughing pass then naturally your finish will not be optimal.

Might be worth considering using double stick tape to eliminate the need for tabs, cure that problem at least.
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Re: Separate Last Pass for reducing tool marks

Postby Adrian » Mon Apr 08, 2019 8:08 pm

Separate last pass has been around for a few versions now in both Aspire and VCarve. It's an option on the profile toolpath.
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Re: Separate Last Pass for reducing tool marks

Postby Rcnewcomb » Mon Apr 08, 2019 8:18 pm

Check the "Show advanced toolpath options" box to have the "Do Separate Last Pass" section appear
LastPass.JPG
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Re: Separate Last Pass for reducing tool marks

Postby Xxray » Mon Apr 08, 2019 8:45 pm

Oh profile, I was looking at pockets. Hmm, never used that option never really had the need I guess.
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Re: Separate Last Pass for reducing tool marks

Postby rscrawford » Mon Apr 08, 2019 9:44 pm

Try using the spiral ramp feature for the profile cut. This does a continuous ramp cut, so there aren't any plunges. Then do a separate last pass to remove any tiny tool marks from the spiral cut.
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Re: Separate Last Pass for reducing tool marks

Postby laflippin » Tue Apr 09, 2019 1:23 am

Ted and Randall, Thank you very much for your concise discussions and advice--I will be trying out your tips pretty soon and will let you know how things work out. By the way, I really am not trying to eliminate the need for finish sanding--like you, I think it is an unavoidable part of good woodworking. But, whatever I can do to reduce the need for coarse sanding to remove glaring tool marks will be very much appreciated.
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