Daniel's Work Thread: Toward a Hackerspace Scanner

[daniel_reetz]

The good thing is that all of our measurements are taken from the top of the bed, not the top of the material, which means that if you mill down to 0.72", you will end up with 0.72". You are setting z=0 to the bed, right?

Yep, I am now...

You can definitely get more aggressive with the ramping. VCarve has options for spiral ramp (VERRRRY LONG) or, I forget what it's called, diagonal ramp? In any case you set the distance the ramp goes over. Try something like 2", since your depth pass is only 0.25" -- so you're going into the wood 1/32" for each 1/4" bit diameter travelled.

I'll be going after this, since this morning's cut took 1.5hrs, way too long.

Another bit of advice: set your pocket's tooling in VCarve to 80% stepover. That should save a little bit of time.

This, too.

[rob]

The cut was perfect, except that I dulled my bit by driving it into one of my brass screws. But that's no big deal.

I got so frustrated with material thickness issues that I made a modification to the design, I think it was suggested a long time ago. Basically I just spec'd the slots to .5". They came out flawlessly.

Those look awesome!

[daniel_reetz]

Here's a video of Dennis P cutting bearing pockets with a drill press:

[daniel_reetz]

So one of the big problems of cutting these things is that when you're done, you have to then go and cut out every tabbed piece with a chisel. It takes a lot of time! Between 15 and 30 minutes. To me, that is unacceptable. I am thinking about ways to cut down on spending so much time cutting pieces out.

Here's an image to show what I mean: these front and back braces are held in by tabs. My current process is to have the machine cut everything out, and then take a chisel and cut these tabs right next to the part, while the entire piece of wood is still on the machine bed. This REALLY SLOWS THINGS DOWN.

tabs.jpg (186.01 KiB) Viewed 550 times

Today I had kind of a funny idea. I was thinking maybe I could add a few 3/4" pieces of MDF to my machine bed so that it is very thick. Then basically cut pockets in the extra-thick bed that could hold each of these parts. I'd cut them out with tabs just as I do now, but there would be a final pass that swoops in and cuts the tabs so that the parts fall into the pockets in the bed. Then I can slide the waste sheet off the machine with no issues and collect the good parts.

It has a few problems, especially that the tabbed pieces might not fall the way I want... but I really want to automate part collection. Any ideas or suggestions?

[jck57]

I'd worry that if you don't have the piece secured, it could bounce around when you're cutting the tabs with the router, even if you have the cut-out underneath. Could you write a special program for cutting the tabs, where the cutter swoops down for each tab and then comes out of the groove? If you could do that, you could have 1/4" wood inserts that you put in the the grooves to act as temporary tabs as you cut out the solid tabs. That would keep the piece from jumping around as you cut the tabs out. The spacers could be scraps of 1/4"x1"x1" Luan.

[rob]

That might work with the larger pieces, but definitely not with the smaller pieces, which will get chewed up by the bit. The smaller pieces are also liable to get pulled by the bit so that when there's only one tab left, the piece shears off at the tab, causing damage.

If you could get it to work somehow, though, it would save a lot of time because then you don't have to sand the tabs off.

I have two methods. What I used to do is take a dremel with a routing bit and cut the tabs off that way. Now, though, I've found it's much faster to use a tiny reciprocating saw. The one I use is pneumatically powered!

[jck57]

That might work with the larger pieces, but definitely not with the smaller pieces, which will get chewed up by the bit. The smaller pieces are also liable to get pulled by the bit so that when there's only one tab left, the piece shears off at the tab, causing damage.

Right. Good point.

If you could get it to work somehow, though, it would save a lot of time because then you don't have to sand the tabs off.

OK. How about this: take some 3/4 x 2 x 2 scraps of wood and screw them through the cut grooves to the sacrificial sheet underneath. The scraps clamp the work down until the tabs are cut, then you pull the screws.

EDIT: Another idea: hand held laminate trimmer with a 1/4" flush cutting, bottom cutting bit. Set the depth to 3/4". With the motor off, push the trimmer around the groove. When a tab stops you, back up a bit, turn the motor on and then zip off the tab. Repeat. Easy-Breezy-Chuckaleezy.

ReEDIT: Use the 1/4 x 1 x 1 Luan scraps from the first idea to keep the pieces from moving around while you cut with the laminate trimmer.

I also would be sorely tempted to go with dpc's scheme and just screw the pieces down to begin with.

[dpc]

If I were doing this I'd come up with some method so that I didn't need the tabs at all. Maybe screw the 3/4" sheet to another sheet underneath, with a minimum of two screws through each part. You'd end up with a few small 1/8" screw holes in each part but that's not a big deal and it would save you a lot of time and headaches.

[jck57]

Re: my previous post, this is the type of router bit I meant:

http://www.ebay.com/itm/Century-Router-Bit-Straight-HSS-1-4-/200723220677#ht_1610wt_908

And because it's high speed steel (HSS) instead of carbide, you can grind the cutting length down to 3/8" if it's too long. You really don't need bottom cutting anyway.

[daniel_reetz]

These are some great ideas, thanks everyone. A bunch of semi-connected thoughts follow. I think screwing each part down might be almost as much work as cutting tabs, so I'm less inclined to go that route. However the handheld laminate trimmer is a new tool in my world (my woodworking knowledge is zero). I could probably modify the trimmer with a peg to keep it cleanly on-track. OR I could even cut a track next to where each tab is so that the trimming goes real easy. Hmm. The only downside is that one side of my machine is up against a wall so reach can be an issue.

I had another thought today, which was inspired by Jck57's idea about the 1/4" strips to hold parts. Basically, I realized that I could make the "inverse" of the part as a very effective clamp. So imagine, say, three 6"wide, 48" long strips of wood. Each one of these strips has a protrusion where there is a slot in the part so that they secure any piece they lay over. They are actually elaborate clamps that lay over top of the cut/machined piece of plywood. In both the cut plywood and the clamp strip, there is, I dunno, a hole or something where a quick release clamp goes so they mount really quickly. The tabs are everywhere that this clamp is not.

So the work process goes like this:
1. CNC route everything with tabs.
2. Install clamp strips.
3. Cut tabs with CNC.
4. Remove clamp strips.
5. Remove parts and waste.

I still like dpc's instinct to get rid of tabs entirely. One possible solution would be to create a custom vac bed that holds each part in place. I do strongly favor that idea but it does make the whole system much louder and means another round of building, so I'm not sure I want to go there just yet.

An even further possibility would be to program the parts to be processed on a smaller, purpose-built machine. So the parts are still in place with tabs, but the machine cuts them all into, say, 2x2 foot squares of support material which are fed into a smaller router or something.