Grf - cnc #2

**seafurymike** · 6th February 2009, 11:14 PM

So for the long story in short, I finally came up with a name for CNC #2 and now I can post the build progress. Really, quite a stupid reason to have held off.

So GRF - "Goes Really Fast"

I thought I would list the parts and supplier for anyone who is interested.

Project Parts:

100 X 50 Extruded Framing - Robot Units (Donated) Tullamarine
Stepper Motors - Ocean Controls Seaford
Drivers G540 - Gecko Drive (Won this at the CNC BBQ)
Smooth Steppers - Homann Design Melbourne
Linear Rails (20mm ABBA) - Linear Bearings in Rowville
Belts and Pulleys - Powergrip in Rowville

The following pictures are as of tonight where I spent 15 minutes adding the gantry to the base frame. I love this extruded systems ability to rapidly join sections. make a mistake or need to adjust something slightly, just un-do it and re-tighten.

Image 1 - 4:1 reduction gear and drive setup
Image 2 - Smooth stepper and G540 driver (got to work through the hook up of these 2)
Image 3 - The gantry attached
Image 4 - Just the rails and end pulleys for the gantry drive belts
Image 5 - Transition plate, which allows the pillow blocks to attach to the gantry
Image 6 - Powergrip pulley and belt for the reduction.
Image 7 - Close up of the gantry connection

The idea is to have the gantry driven by a continuous belt, which is reduction driven from one end via a drive shaft to the end pulleys. I have seen this setup on Frans's router in Canberra and it worked quite well. I felt this was a simple system to employ and maintain. We will see if I have issues with the gantry skewing. If this occurs I will drive both sides with a stepper motor for each side and sync it with electronins like Greg does on his unit.

The versatility of using the Robot Units extruded sections is great. The system provides for self alignment due to the nature of the joints. Plates (the black ones seen in image 1) and the locating grommets which sit in these plates make sure that everything is 90 degrees when it gets bolted together. Plus the fact that we computer cut each length exactly. The joints provide for 4 tonne shear strength, so no worries with it coming apart in a hurry.

I still lack some linear rails for my Y-Axis, but i will purchase these soon. I have a Z-Axis already, which i acquired from Ebay and so a transition plate is needed, which i will machine up at school soon. I also need to devise a methos to connect the drive belt to the gantry, I will se what I can come up with for this.

I will be running 48Vdc as this is a supply I had handy from work. Mach 3 will again drive the system.

Okay thats enough ranting for now.

**rodm** · 7th February 2009, 10:31 AM

Nice work.

I have responded four times and the site isn't posting my reply. I'll try later with a couple of suggestions.

**Greolt** · 7th February 2009, 12:13 PM

Looking good so far Mike. That aluminium profile is great to work with.

Wish I could justify a few lengths of that profile in the 5th pic to make up my router table. Nice and heavy.

Is there any way you can increase the rigidity of the union of those and the gantry uprights? Perhaps a triangular flat plate on the inside. (think it looks flush)

Also like the way you have tied the belt drives together on both ends by using a full length shaft on the idler end.

Perhaps you might want to make some brackets and move the outer pillow blocks out closer to the pulleys. Better support of the belt tension.

Keep us up with your progress.

Greg

**rodm** · 7th February 2009, 06:58 PM

Have to agree on the plate connecting the upright of the gantry to the rails. The lever effect of the gantry will apply a lot of pressure on that joint. An easy fix though.

Also suggest that you place the Y axis rails on top of those aluminum rails so that you keep them clear of the sawdust and bring the Z axis closer to the gantry. Building outwards may result in the spindle overhanging the front of the table and you get a canterlever effect on the gantry.

**seafurymike** · 8th February 2009, 02:46 PM

Thanks guys for the feedback.

Gantry:
The gantry has 8 bolts each side connecting it to the transition plate.
The 4 main bolts have a 4 tonne shear strength and I added the two extra bolts via the black bracket just for luck. I expect this is over engineered and shouldn't rock.

The main concern I had with the setup is that I made the plate only 200mm long. This is a slight comprimise as too long and I loose X-Axis cutting and too short it will create a pendulum effect whilst cutting (I find this on my 1st router).

Greg, I think I could bolt a plate on the inside of the gantry which ties the gantry to the transition plate. It might be a bit of overkill though.

I have included a close up of the transition plate and gantry showing 1 bolt inserted into the black plate and the other side without. It also shows the 90 degree bracket that was added for extra support.

Question 1:
I like the idea of running the Z-Axis off of a rail on top of the Y-Axis. Rod, where have you placed the bottom rail for this. I have tried looking for your build log, but could only come across some photos of your setup in other threads, which only show the top rail.

Question 2:
Has anyone got a wiring schematic which shows how to connect the smooth stepper to a G540? or other geckos?

**rodm** · 8th February 2009, 03:59 PM

Hi Mike,
How is the black end plate fixed to the gantry vertical?
In any case the materials you have chosen make it easy to add gussets at a later time if you find the connections need strenghtening.

I would place the bottom rail on top of the rail as well or if you are concerned about flex then underneath but make sure the linear rails have seals. Placing it on top of the rail would work if you made the conecting plate to the Z axis hang to be flush with the bottom of your aluminum rail.

There are other design options like fixing the rail at the bottom rear (my preference for my new machine) but what I have described is the simplest.

**seafurymike** · 8th February 2009, 05:53 PM

Rod,

Bolted in with an M8 screw/nut arrangement. I think it will be easy to manufacture a plate as Greg mentioned. I think i will progress with that just to be sure.

So I have drawn the 3 options that you have described. From each I see benefits, but I think Option 2 would be the simplest to manufacture, which provides adequate dust protection (especially with a good table vacuum system.

**rodm** · 8th February 2009, 06:25 PM

Hi Mike,
Option 2 is the strongest having the greatest distance between the linear rails and the box section connection will be the most rigid. The only issue is making sure your box is exactly the same internal dimensions as the mounted trucks. You might want to think about how you will make and assemble this before you start. An option would be to make it slightly oversize and shim out to the trucks.
To partially shield the lower rail you could fix a piece of light ally angle off the bottom of the ally rail and in front of the linear rail just clearing your box. Another cheap option is a brush type door seal from Bunnings.
I am a bit paranoid about shielding the rails as I have seen a few machiners where MDF dust has entered the trucks and siezed them. In one case a hammer was required to remove the trucks from the rails.
I have tried a few vaccum systems and none have been successful. The reason is that once a vacuum enters the open air it is not very strong at all. Try placing you hand over the end of a shop or house vacuum pipe. Move it 25mm away and you can hardly feel any vacuum at all. The 100mm workshop dust extractors work much better (high volume/low vacuum) but a 100mm pipe hanging off a medium sized machine is just to bulky IMHO.

**Zoot** · 8th February 2009, 07:03 PM

Mike,
I know nutting! But will throw my 2 penneth worth in!!

I am about to build my gantry and I have attached a copy of my cross section ... at Rod's suggestion, I have one rail on top and have tucked the bottom rail around the back, hopefully well clear of mdf dust ... certainly frightens you when you hear of guys having to hammer the trucks off the rails!

Cheers,

Alan

**seafurymike** · 8th February 2009, 07:49 PM

Thanks Alan,

If nothing else, i love the idea of also having the screw mounted on the back plate and driven from there. The other great thing with using aluminum extrude is that when you screw the rails down, they are parallel all the way. It's great stuff.

/M

**seafurymike** · 8th February 2009, 08:41 PM

Rod,

The reason i said dust extraction was when I saw Frans's router he had the setup in the photo, which as you have also indicated caught quite a lot of the dust. The frill around the collector is the dust/water reducer that mounts to the side of 18 wheeler trucks. He cut it down to suit. Similar to the brush type door seals i suspect.

Point noted with the use of shims

**seafurymike** · 9th February 2009, 08:34 PM

Did a little more work tonight and I have been able to mount the Y-Axis rails and tie down the gantry.

I made some measurements and the next task is to start the Z-Axis mounting plate.
A job for thusday at trade school.

The Z-axis is as I mentioned an ebay item. Although it is 80mm wide, I have to make the plate 130mm as I can't get the pillow blocks any closer. Bit of a shame in that it reduces the cutting area, but the positive is that it will add stability.

Pictures enclosed, sorry about the blurry shot.

Thanks for all the feedback guys. Will keep these points in mind.

** I hope all this hard work doesn't go up in flames. Damn fires.

**seafurymike** · 15th February 2009, 08:22 PM

Well I got a bit more done this week and spent yesterday mounting my plate and the Z-axis.

I managed to slide the Y screw in this afternoon, so i can take some measurements for brackets that need to be made next week.

Still need to think of how to mount the stepper to drive the linear screw.

A few pictures as everyone likes to look and not read.(at least i do)

**rodm** · 15th February 2009, 11:34 PM

Hi Mike,
Coming along nicely.

**seafurymike** · 16th March 2009, 08:44 PM

It has been a while, but i have been hard at it.

I have a new frame which now has the CNC router sitting on top. I still need to attach this to the frame with bolts and a glue.

I have fitted the x-axis and re-fited it again with upgraded cross-rods as i was finding flex in the rods caused the belt to run off the pulley. I knew i should have gone the 20mm from the beginning.

I have also fitted the Y axis to the ball screw. I made a new connector plate which attaches to the nut. This seems to work quite well.

The Z- axis has been mounted to the Y-axis and I still need to connect the wires to the motor, just as I have with the X and Y axis. I tried to make it all neat by housing them in little gray boxes.

Along with the mechanics, i have hooked the G540 unit to the smooth stepper. I have configured my laptop to drive it. I mounted all of this into the box situated at the base of the router, with the 48Vdc power supply. I added some connectors to the front plate which will allow me to hook up each of the axis and i also added a DB25 which will be used for homing switches and limit switch connection back to the G540.

I re-fitted the DC fans in the box to AC fans which i had lying around. This will keep the hottest unit cool. I will add some filtration pads when i get a chance to limit ingestion of foreign matter. The air is drawn from right to left, so i housed the power supply on the left, close to the fans as i thought it would generate most heat.

I am now in the process of setting up each axis in Mach 3 so it runs smooth and accurate. Once I get my X and Y axis sorted i will go back and finish the Z-axis by connecting in the motor and making a mount for the router.

In the interim i will machine some end caps for the belt pulleys to make sure the belt does not come off.

/M

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