Neil Rosenberg published a new build:

Read more about this build...

 

Thanks Mark. I placed a large order with OpenBuilds today. Only thing in short supply was the eccentrics, hopefully more on the way...

TTYL!

 

Hi there Nick, thanks for the follow-up.

The z-axis rack and spur gear are from SDP-SI.com, part numbers S1811Y-RC-1 and S1086Z-024S016, cost at single unit qyt is $57.44 and $18.57 respectively. They are both in stock. The spur gear is .25 bore, good for the NEMA 23 motors I chose.

Also there are three full-length 20x40 vbeams running the long direction, mounted with angle brackets for stability. Here's a screen-shot of the underside (brackets are not yet shown in the model):

 

Oh another comment -- the "spoiler board" is going to become a vacuum table. There's a neat video on YouTube by Sean Martin of DonekTools:



I don't think the vacuum table needs to be as thick as what he did -- there's really not much airflow, in fact almost NONE during operation, otherwise it won't draw down the parts. Mine will probably be about 1/2 as thick as his. I like his idea of putting a sacrificial layer on top, but I'd probably screw it down rather than glue it.

Also, at about timestamp 6:58 there's great footage of (I assume) his kids helping him build a CNC Mogul CNC router. I almost bought one of those, but there was just too little information on the web page (http://cncmogul.com/) and besides, I really wanted to roll my own

 

I'm playing with different ideas on the construction of the vacuum table, thanks for the suggestions. It may work to have the vacuum box provide most of the long-direction racking stiffness of the machine. Perhaps I'll remove the three lengthwise 20-40's, nestle the box in the open space, and attach to the end rails high and low. Just need to avoid the motors...

As far as the vacuum itself, that's a good thought to add a "leak" hole at the end away from the hose (I may make it adjustable somehow) -- don't want to burn out too many shop vacs

 

Updated model available, now has a start at some of the ideas above.

 

I can provide any format that SolidWorks can export.

I have a few more days of detailing, then I'll post them. Let me know your preferred format please. They will probably import as uneditable but you'll be able to get all the dimensions and details.

Also FYI there's a free SolidWorks eDrawings Viewer that may allow you to view the models I've already posted. Here's the link: http://www.edrawingsviewer.com/ed/edrawings-viewer.htm

Neil

 

Similar to how Sean Martin (Donek) did it -- drill the current (shown) permanent top with a matrix of holes, attach a sacrificial spoiler of MDF on top, glue and use vacuum as a hold-down. Once dry, re-drill the same set of holes, but this time through the MDF. Then surface skim the MDF in place to true it to the machine.

The MDF spoiler can be skim machined as needed. When it gets really thin I'll replace it, re-drill and re-flatten to get started anew.

 

Good thought, thanks.

 

I am now building the Frog, going well so far. I plan to post some photos soon.

BTW I have just posted an updated version (1.3), now includes provisions for a belt tensioner for the dual-motor X axis, plus holes in the end plates to allow the belt to "escape". Makes life a lot easier. I'll put up photos of that as well.

As regards John89702's question, I've been trying to enable measurement in SolidWorks, but no matter what I do eDrawings doesn't seem to see it. I was however able to import the .sldprt files into Inventor 2013 and measure from there. Perhaps other packages can do the same?

I will be happy to export any of the parts files in whatever format you need (iges, dxf, stl, etc.) -- just say the word.

 

Apparently I need to have SolidWorks Pro to enable measuring, sorry. I have the Standard version.

In the meanwhile, my offer stands. If there's a request for an export of one or more parts, I'll be happy to provide.

 

Thanks Mark

It's coming together pretty fast now. I've already checked the electronics, time will tell if this $58 4-axis Chinese/Ebay driver board will be a boon or a headache. Seems ok for now, but the proof is in the cutting. I already fixed a tiny solder blob on it that prevented 2-directional travel on one of the axes. Mach3 is great with it, easy to set up.

BTW I'd like to share a bit of feedback with whomever about a few of the OpenBuilds parts. Nothing earth shattering, but perhaps I can help improve things for others. We can take this offline if you like.

Also I have concerns about the GT2 glass belt for my y-axis. Seems pretty lightweight, I wonder how stretchy it is. Do you have any data? I ordered a Gates polyamide (Kevlar) GT2 belt -- when I get an opportunity I'd like to do a bit of A-B testing vs the glass belt.

Neil

 

Been looking for the 3mm pitch GT2 belts and pulleys, seem to be pretty rare. Do you have a good source?

 

Thanks Matt, I'll have a look.

I did my first cutting today, very exciting! Showed me all sorts of things that I need to do better, starting with the right speeds, depths of cut, material stabilizing. I also had to do some revisions in Mach3 to the acceleration ramps and maximum speeds of the various motors to eliminate a bit of jerky motion. I'm running 1/8 microstep on x and y, 1/16 on z. On paper this gives the system .001" granularity or better, but I'll be happy with .01" to .03" accuracy in actual use.

The good news is that the electronics and software performed flawlessly, and after some fussing with the bit mount (kept wanting to loosen up) I was able to get clean repeatable lines. Every indication is that with good bits and proper speeds it will do quite nicely. However, this is no Bridgeport knee mill; the speed and depth of cut can't compare with an industrial strength machine with leadscrews everywhere and massive frame components. No surprise here.

I do have some concerns about the lightweight trim router that I'm using, it's a new Horrible Freight model 44914, cost all of $30. It emitted a fairly strong burn smell, but in truth I did abuse it at the start, even stalled it once. I also had difficulty getting it to tighten on a few of my 1/4" shank bits. Cheap is cheap, I guess. It did work well eventually once I got my bit mount and speed/depth worked out.

Onward!

P.S. I also see that my grab bag of old routing bits will *never* do -- love the smell of burning wood (NOT!). Anyone have a favorite source for routing bits, good deals, etc?

 

In response to Matt -- the motor I stalled was the router itself (the high speed cutting motor), not one of the steppers. As I mentioned, I had a bit wander out, and it started to gouge the material. It was too much for the weeny motor to handle.

I haven't yet noticed dropped steps or accumulated error, but I do keep the belts tight and don't try to accelerate the steppers faster than they can handle. That being said, it's early yet. The Nema23's I got are 270 oz-inch, 200 steps/rev, 3 amp. I'm running them at 75% power. Plenty strong, any more than that and the machine would start to tear itself apart if it jammed.

I'll post the gantry and side plates in DXF by tomorrow, thanks for asking. I will also post a few other custom parts that may be useful. I cut these out of aluminum on a CNC plasma table, then post-machined for accurate holes.

Mark, thanks as always for the encouragement. Means a lot to know there are folks like yourself who have "been there" and are willing to lend an ear!

The router mount (with hose clamps) is really rigid, that puppy's not going to move. It was nice that the particular router has a true cylindrical shape, fits into the middle groove of the V-Groove, keeps it aligned. The (4) brackets are plasma cut and bent up, one-screw mount to the extrusion with a Tee nut. I cut the straps into two pieces, looped the cut ends through the brackets, then back on themselves. I also cut off excess length and put electrical tape over the cut end, it's pretty sharp:



For those who may be interested, the belt tensioner is similar in concept to strap tighteners that have been used on backpacks and etc for years. The belt exits from the chassis through a hole I milled into the support plate, once around the slots, and then I tuck a short end back into the chassis, locks on itself that way. The screw tip has been ground into a dull point, fits into the head of the nearby screw (to keep it in place). Here are better photos, one is a screen shot from SW (minus hardware and belt):



Also, thought I'd post a photo of the "drag chain" that I used on the carriage (there are two more under the chassis). I've not used them before, I really like them for keeping the wires out of harm's way. Also, I used Cat6 24 awg cable for the step motors, with like-colored wires paralleled (4x2) for greater current capacity:



Thanks for the leads on the 3mm belts/pulleys (and router bits). I will probably pick up some of the 3mm stuff soon, glad you're adding it to the store. I'll email you separately (as promised) with parts feedback and a few other items you may consider for the store.

Be well
N