A plastic JGRO

[uspl]

Hi all

After lurking for a long time and coming out of the winter slumber, I decided to bite the bullet and do the JGRO build.

A couple of variations:

• Most of the framework is made from 20mm thick HDPE (the stuff chopping boards are made from).
• The bearings are a mix of 20mm and 12mm linear pillow block bearings on ground shafts

The HDPE is brilliant to work with. It doesn't split, you can cut, drill and tap it like aluminium or steel and is is impervious to moisture and hence swelling or moving like MDF.

So far I have built the base framework (though that is in MDF and needs to be painted) ready to take the gantry and today finished the Z axis and router mount.

I am driving it all with Mach 3 using the custom ROUTER screen.

Photos to follow in the thread and all comments welcome.

Cheers

David

[uspl]

• X Base framework
• Z mount in HDPE
• Electronics box

[gully]

Nice work David,
Good luck with the rest of your JGRO build.
I will follow along as you post your updates

Gully

[Rotax91]

Looks very nice. The 20mm rods are exactly what I was referring to in another thread and why more people aren't using them. I email VXD on Wed and they said they could support 300lbs.

Question: It looks like your adjustment blocks are 'fixed' unlike normal JGRO adj blocks. So did you make the holes in your front & back frame exactly 20mm as well? If so, how did you drill the holes so the front & back frame holes were exactly the same distance apart to avoid any binding in the linear bearings.

[bobsch]

Looks very nice. The 20mm rods are exactly what I was referring to in another thread and why more people aren't using them. I email VXD on Wed and they said they could support 300lbs.

300lbs. over what span?

[Rotax91]

The rods I inquired on were 60" in length. The auction was on ebay.

[uspl]

Looks very nice. The 20mm rods are exactly what I was referring to in another thread and why more people aren't using them. I email VXD on Wed and they said they could support 300lbs.

I got the rods from a stainless steel wholesaler by going to the trade desk and asking to look in their scrap bin. They are 20mm 316 stainless and at 1 metre long cost me $10 each. The pillow bearings were $5 on eBay.

Question: It looks like your adjustment blocks are 'fixed' unlike normal JGRO adj blocks. So did you make the holes in your front & back frame exactly 20mm as well? If so, how did you drill the holes so the front & back frame holes were exactly the same distance apart to avoid any binding in the linear bearings.

When I was prototyping this setup I made a few small scale mock up gantries and beds and yes, the alignment issue came up. I only have a very limited home workshop but one thing I do have is a nice drill press. To get the alignment right I cut the front and back plates using a Triton table saw so that they were identically sized. Then I bolted them together with temporary fixings and drilled 3mm pilot holes right through both pieces.

For the rear plate I enlarged the holes to 20mm for the rods and 10.5mm for my all-thread to have a bit of clearance. On the front plate I did the same plus made the motor mount hole 32mm to take the Lovejoy coupling.

My workbench is nice and flat so I then laid out the pieces and used a picture frame clamp to make sure they were square before screwing them together.

I loaded a temporary gantry plate with 10Kg of dumbell weights and my little stepper drives the x-axis over 800mm with no binding at all. What look like JGRO adjustment blocks are just retaining collars to keep the rods in place.

Cheers

David

[leaveme]

Why not use the bearings in open type? Price is basically same and you can then add suppot to the bottom of the ground rails.

My build is not a JGRO but X base looks similar. I used a screw in combination of two nuts from the base plate in every 8" distance and it is touching the rail. I then used slight epoxy on the screw top at touch point. It now acts like a supported rail. :-)

[Rotax91]

Hi David, Thanks for the info. I just ordered 20mm 60" linear rails off ebay for my Y axis and 20mm linear bearings like you as well as a forstner bit. I'm gonna build my Z first until I get a bench built to put it on. Question, have you decided what lead screw you are going with. 1/2-8 2 start seems to be common. I want to go with 380oz steppers.

[uspl]

Question, have you decided what lead screw you are going with. 1/2-8 2 start seems to be common. I want to go with 380oz steppers.

My Z & Y axis are on 12mm rod since the Z has virtually no load and the Y will be lightly loaded since I am cutting MDF and plastic with a micro router (laminate trimmer).

As to threaded rod, I am just using all thread 10mm diameter and 1.5 turns per millimeter. The nut is HDPE drilled and tapped to suit. My motors give me 320mm per minute of travel. Yes, it is chronically slow in the real world of CNC but they will do for this project.

Cheers

David

[uspl]

Well the Y Axis is done and mounted.

The HDPE is really working well as a construction material, so easy to get a great square and flat edge plus being able to drill and tap it to take socket head screws for easy assembly and no slop if I take it apart 10 times.

Tomorrow I will mount the Z axis, set up the motor and start some dry runs with alignment tests and so forth.

I picked up a $2 laser pointer from the local discount store and am going to mount that in the router bracket. I figure by then getting Mach 3 to do a series of moves and return to zero, if the little red dot is back exactly where it started them I am half way there.

I also learned one of those lessons that you must learn when doing this sort of thing. I was having some issues with the motor not performing quite as expected so hooked up the CRO to the driver board to check the pulse signals were what I was expecting. Memo to self; never unhook CRO leads while the driver is running. Caused some sort of spike and fried a $80 driver card.

**** !!!!


Photos to show where I am up to

Cheers

David

[Rotax91]

Very, very nice work. Thanks for keeping up to date with your progress. I've been following your thread. As I stated above, I ordered some 60" 20mm rails. Also some linear bearings like yours. After alot of reading, I don't think I'm going to use the full 60" like I planned. In research, I found that I would have to much deflection with unsupported rails. I downloaded a program that also calculates deflection over a given distance. The program is called 'beamboy'. What is the length of your Y-axis? I'm thinking of shortening those 60" rods down to 37-40".

Also, what size motors did you go with?

Keep up the GREAT work.
/tim