My first build (yet another jgro)

I've been trolling the forum for a couple weeks reading up on the jgro and decided that its totally within my skill level and would do everything that I want it to including making parts for a larger machine eventually. So with the complete set of plans downloaded, printed and nearly memorized (I've really been into this...) I just went to Lowes for my 1/2" and 3/4" mdf, cut all the straight cuts on the table saw last night and started predrilling holes for the support assemblies.

Everything I've read on others' build threads has been really informative and I'll be keeping a running total of what I've spent on materials. Thanks everyone for the info you've all provided, I look forward to comments as my build thread continues.

Total spent so far on just mdf is $58

Looks like you are well on your way. Do you know what electronics you will be using? Best of luck on your build.

Keith

I'm planning on 305oz steppers and the proboard kit from hobbycnc... I found quickly that no matter how big the predilled hole is drywall screws DESTROY mdf. I've got plenty of left over pieces to recut the small base support pieces that I ruined and back to Lowe's for wood screws I guess.

Yeah it's going to be tough with screws. I used a brad nailer just to hold it together until the glue dried. You could possibly just use glue and clamps, but it would be tricky getting everything aligned without some type of fastener.

Keith

If you don't already own one, pick up a countersink kit while at the hardware store. When running the screws into the MDF, set the torque on your screwdriver to stop turning when the screws reach the bottom of the countersink. Glue won't hold everything together, by itself, once the machine is up and running; the joints will fail and that would make a mess. Almost everyone has made their torsion boxes first thing. If I were to build another JGRO I would wait until after I had the two end pieces built and my adjustment blocks in place. Then put your newly purchased gas pipes into the adjustment blocks and build the torsion boxes to fit the space. There are quite a few really neat ideas on how to negate the sag that will occur, figure one of those into your build. Good luck, and keep posting. Tom

It's been awhile since I built the JGRO, but if I remember there were alot of 1/4" fasteners throughout the design. Some were important and others, not so much. I know that others probably have alot more experience than me, but a properly glued joint in raw, unpainted MDF is strong. Depending on the location and fastener application, the additional strength the fastener adds may or may not be needed. I glued (standard wood glue)both torsion boxes and brad nailed them together. I also glued all the parts for the Z axis together with only alignment pins and clamps. After completing the construction, a good sealer and/or paint are a must to maintain the integrety of the MDF. It gets very "weak" when it is exposed to humidity or liquids. I must admit I didn't use the Jgro very long before I built the Joes 2006. Although it is not exactly compariable, it is made from MDF and uses very few fasteners. If done properly, as Tom mentioned a countersink kit, the combination of fasteners and glue would probably give you the best joint, but in my experience a good glue joint would probably suffice. For me, building the Jgro was a learning experience and it allowed my to understand how cnc routers work (software, electronics, etc), but I quickly realized that I wanted a larger, faster, more rigid machine, so I used the Jgro to build the 2006. This hobby is fun and I hope you enjoy it as much as I do.

Thanks guys, I got a chance to spend a beautiful day holed up in the shop, the brad nailer worked like a charm and I used wood glue on all the joints too. I used heavy duty decking screws to attach the torsion boxes to the sides and the cutting bed, this assembly is really solid. I'm getting excited and I can't wait to bring home the angle aluminum, pipe, and bearings tuesday night and get something to actually move. I'm definitely going to let the machine cut the slots for the clamping hardware when its all together.

Looks really good. You will be making chips in no time. I attached the sides to the bottom in exactly the same way. I've never taken it apart, but I do have the option.

When you get to the bearing assemblies, make a jig to ensure you drill the holes the same distance from the edge. That has to be exactly right for all the bearings to properly contact the pipes. I didn't do that and had to remake them later.

I'm a day behind on getting my pipe and angle aluminum but I cut and drilled all the small mdf pieces yesterday. Just need to get a bit of 1/4" mdf for the one part that requires it, don't recall which part at the moment. Any tips for threading the holes in the mdf? I've read to drill it, fill the hole with ca glue or epoxy and redrill before tapping... I'd like to do it right the first time without splitting my adjustment blocks.

I originally built mine with mdf, but they did not hold up. I drilled and tapped the holes then applied ca to the threads. I still split some of the parts. I ended up replacing all of them with plastic (HDPE -i think). Others have used hardwoods with success. I would save yourself the headache and make them out of something besides mdf.

I wouldn't bother using mdf for the adjustment blocks. If you can get HDPE use that. I couldn't so I used scrap oak that I had. It worked fine. I just drilled the holes slightly undersized and then used the same bolt that was going in to tap the threads.

Between the recent cold snap and a school project to raise funds for local charitys I didn't do much on my jgro in the past week. I drilled mdf and filled the holes for epoxy and I'll try tapping them in the morning before work. I got my 1" pipe for the y axis rails and I'm going to scrap some yard sale roller blades for bearings to start. I downloaded freemill but haven't even installed it yet.
The pipe cost $20 at Lowes and that brings my total cost so far (not including the tap set) to $78.

Any suggestions for an inexpensive or free cam package besides freemill or any comments on freemill?

I've never used Freemill but a great free route would be Sketchup with the Phlatboyz CNC plugin. I've used it before and it works well.

When you get the CNC up and running don't forget to surface the table with the CNC itself. You may have to do it every now and then. I can't believe how much mine sagged considering it's a torsion box.

I'm using solidworks, don't ask how I got it... I'll try the sketchup plugin and see how it works. After reading a post on a model airplane forum about threading mdf I gave it a shot, drill with the right size bit, spread epoxy in the hole and after it dries it threaded great, no splits, the bolts hold tight...

Sounds like a neat idea with the epoxy.

If you have not already done this, you might give it some consideration. A "torsion box" is only fully completed with both a top and bottom to it. If you glue and pin a bottom you will get far less sag to your finished product. Of course this does not reduce the sag of the gas pipes. Tom

Y axis pipe adjusters are mounted and the pipes are trued up. Man there are a lot of holes to drill and tap for the gantry assembly. I spent yesterday cleaning up the shop with hopes of maybe using my benches for more than tool storage. The wife brought home some unclaimed bookshelves from when she taught high school woodshop and I hung them on the wall to reallocate some of my mess. I'm a bit surprised at how deep my piles had become but I've also found a ton of clamps.

Why drill and tap all of the screws? I only did that for the adjustment blocks and used drywall screws with glue for everything else. For the gantry I added biscuits to help align it.

I haven't had much luck using drywall screws in mdf without splitting, just getting the pilot hole size right has been a nightmare. I'll try with some scraps and see how solid it is or if i can even do it without splitting, I'd hate to ruin the pieces I already.

well... the epoxy trick only worked for the large adjustment blocks, I put epoxy in 4 of the small adjustment blocks and they all split, the other four tapped without any issue, go figure... I got the 1/2" pipe and mounted my x axis rails, finished the gantry assembly and got everything rolling in the y axis, I found 1 1/4" weld angle at lowes and its stronger and have the price of the aluminum angle, just harder to cut and drill. the y and x linear bearings are done, the x axis carriage assemble is almost done, I got tired and confused and cut 1/2" off the x axis nut support before I realized that I had bolted the top and bottom plates where the bearing mounts go and eventually i figured it out.

the next steps are to make the z linear bearings, make 4 more small adjustment blocks, make a new x axis nut support and get some $ together for motors and delrin...

spent another $80 on pipe, weld angle and fasteners bringing the total spent so far to $158