24" x 80" cut area, 8020 build...

Just getting started, after browsing here for years, and a few false starts, the time has come.

After seeing Fine Line Automations 2' x 3' build, and talking to Ahren at cncrouter parts a bit, I started ordering bits and pieces.

My goat is a cut area of at least 24" x 80" as I'll mostly be using this to cut molds for model airplanes. Figuring for most everything I'll do, this is the general 'needed' cut size.

Another consideration is limited space. I'll actually be adding on to my little work shed to make room for this.

Because of the longer X axis need, I am going with Ahren's new rack and pinion drive (one on each side). Based on the video's of his system in operation:

http://www.cnczone.com/forums/showth...t=77372&page=6

I am working on drawing up a system where the rails will have supportive legs like his demo, and the Y axis will ride right on top of the x, with the Z dipping down. Seem's a lot less complex considering I'm basing it around his R&P for the X.

I have my G540 as well as steppers, and some pieces coming, but need input on what might be the 'bad' part of such a design... and once I have it tweaked out, it will be time to order the 8020 and remaining bits from Ahren.

This is just an initial drawing to give an idea, remember there will be legs on the x axis's...

Arbo,
Looking forward to seeing this come to life! Your parts should ship Tuesday, and arrive at your place on Thursday. Keep up the 3D modeling -- it definitely helps to avoid trouble down the road.

Best regards,

Ahren
www.cncrouterparts.com

Will do. Do you think the concept is ok?

Also, what is the required 'overhang' of the 1/4" steel for clearance? 1/2 inch?

For the y carriage, is it better to have a wider piece of steel for stability?

Thanks
Paul

Paul,
Yes, the concept looks like it will work well. Just don't try to get too much z-travel out of it (I'd keep it at 8" or less) -- this is the only cantilevered axis in the system, so it is usually the weak point. And yes, the required overhang for the R&P is 1/2".

For your Y carriage, wider steel can be helpful, so you might consider a 6" or so wide piece. Depends on the z travel you're going for.

Best regards,

Ahren
www.cncrouterparts.com

I'd like at least a good 5" travel, I don't think I'd have a need for much more than that. I'll definitely go with wider steel for that rail as I figured it would make it more stable. I was considering using the extended carriages as well rather than the normal ones figuring a wider 'base' would be better.

I'll have to play with the z in CAD a bit more.

Got my hands on some used 1530. WOW, much more weight to it than I thought, and far more stout.

Now I must keep myself from hooking up my steppers to the gecko drive to play and continue with the CAD. ;)

Ahren,

I have a few questions about the z setup.

For the one on the 2' x 3' machine, what is the useable travel on such a setup?

It seems the way to extend the travel is lengthen the 'top' part of the configuration, and have a plate like the one you make where it is longer towards the 'bottom' with the router mount holes moved down. Is that correct?

Also, would there be any advantage in going to 6" steel vs 4" in terms of side to side movement?

Thanks
Paul

Arbo,

With the current z, there is about 4.5" of usable travel. You're exactly right about extending z-travel. You can go higher on the rail, and make a longer cantilever for the z, but don't get too aggressive with this approach if you want to maintain stiffness. As for 4" vs 6", I don't think there's much advantage to going with 6" here -- the z is already wider in that direction.

An alternative to the above approach is to make a custom plate that spans the carriages on the gantry, but also allows you to mount the z carriages and z nut to it. This would have the z rail, extrusion, motor and bearings moving up and down, and provides probably the stiffest z for longer travels. However, I don't sell that plate, although I've been thinking about it. Designing it so you can adjust 2 ACME nuts and 4 carriages while keeping things square is not an easy job. Plus you still have to make it :). Let me know if you're interested in this, though, and I can provide some more details.

Ahren
www.cncrouterparts.com

Perhaps I am confused about 'usable' travel. With the z all the way up, it seems the bit must be lower than the lowest part of the z assembly, correct?

If that's the case then usable would be from there, to as far down as the z can travel.

If not perhaps I'm missing something.

Arbo,
You've got it right. The 4.5" is just what's available in the current version of the plans (with about a 10" piece of CRS on the z). It's a little dicey to define, since as you have alluded to, the length of the bit you put in can impact how far you can move. So in some cases, usable travel is defined as the distance from the lowest hanging portion of the z in the "up" position (which may be the bit) to the lowest achievable position you can get to.

Ahren
www.cncrouterparts.com

That's what I figured. I think for simplicity, I'll be using that design Z, with the only changes being 1" longer steel rail, 1" longer 8020 (towards the top, mount to the Y at the same location) and modify one of your plates to allow to drop it 1" 'down'... that should give me theoretically, 5 1/2" of Z.

now to put those dimensions into CAD.

Of course there will be cross pieces at the bottom of the legs to keep the x's solid, I'm guessing end pieces across the x's as well.

Now to see what might be wrong with the idea, or what might need changed.

as for usable dimensions, I figured x is just over 82", y just over 24" and z is ~6 inches.

Look how far down I had to move the router mounting plate though... seems odd, but moving it all the way up, the 'bit' would be at the just below the bottom of the z carriage, and going all the way down provides 6"...

yeah, I'm missing the lovejoy connectors as well as the end bearing blocks...

Paul,

Every bit is going to have some length to it -- I don't think I have much of anything that doesn't hang out at least 1". Really, you just need the shortest bit you're planning on using in the router to be even with the bottom to get maximum travel. Also, looks like your router doesn't hang down in the mount as low as some. Combine all that with the extra travel you're shooting for, and I think that's the reason for you extra overhang.

Your design is looking really good. It's fantastic to see someone take the time to design a machine thoroughly in 3D. I think you'll be very pleased you went this way, as it will save you a lot of trouble down the road -- keep up the good work!

Ahren
www.cncrouterparts.com

PS Your parts should get there today if they aren't there already. Get psyched!

Yeah, if I could find a 3d cad version of a commonly used router and the mounting pieces I could be more accurate. That one is the only one I found online (don't even remember what it is).

One thing I worried about was the bottom gear on the R&P hitting the legs, but I'm hoping it doesn't stick out that far. If you could set the rack on a piece of 1545 and it won't hit, I should be good, was hard to tell from your video's.

The whole lovejoy connector as well as the other pieces to hold the rod in place seem like they take up so much space to me. I've been wasting too much time looking to see what else might work that would require less space.

Is there any reason a direct 1/2 to 1/4 coupler wouldn't work, or would be a problem?

and does the acme rod need that extra support, or is that mostly to hold the lovejoy connector in place?

Quote:

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Originally Posted by Arbo

Yeah, if I could find a 3d cad version of a commonly used router .................

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I modeled a PC 892.
http://www.cnczone.com/forums/showpo...&postcount=972

Paul,

You should be fine with the gear and the legs -- it's designed to have a very minimal clearance.

As for the coupler, you definitely want the thrust bearings and clamps around the bearing block -- otherwise your motor bearings end up absorbing the thrust load, which is not good, as they aren't designed for these sorts of forces. However, you can potentially thread the ACME directly through the bearing block and skip the drill rod to save some space. The only issue with this is that the thrust washers sometimes fall down in the grooves of the screw, which is not so good, People have gotten around this by filling the threads in this portion in with epoxy,

I also now have helical couplers (1/4 to 1/2) for sale that are shorter than the lovejoys and zero backlash (Lovejoys have about 0.002" of backlash). I'll put them up on the site today.

Ahren
www.cncrouterparts.com

Quote:

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Originally Posted by ger21

I modeled a PC 892.
http://www.cnczone.com/forums/showpo...&postcount=972

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Nice, thanks. Yeah, that makes a lot of difference, the plate can now go where it should, and it it just shy of 6"of travel.

now that I have the basic idea down, I'll get busy getting it together with bolts and all. ;)

Will use your couplers as well. I like that idea better than the lovejoys.

I guess another dumb question related to the rod drive setup, why not use 2 1/2 collars, rather than one on one side and the bigger one on he other?

Hoping the 1/2" collars are good for both sides, I re-did the z.