[prcdslnc13]

Hey Guys! Im still pretty new to the DIY CNC world, but I am a CNC programmer at one of the largest manufacturing companies in the US. Ive been lurking on the forums for about 6 months now, and I built a RockCliff machine about 5 months ago. I love the machine and it works awesome, but being a guy and such I wanted bigger and more power about a day after I got it running :cheers:

So being that Im around giant machines all day, and working with some great mechanical minds Ive spent some time making up my own version of the fixed gantry, with some inspiration from alot of the other MDF and DIY builds.

Space was a big concern with this as my workspace is a one car garage, that the wife would still like to park a car in. But I wanted to be able to cut 48" wide boards at the least. So after some thought, I decided to place my gantry over the long axis of my machine. The axis will travel on v-groove bearings on angle aluminum and be driven by roller chain. The gantry is about 60" long so I thought chain would help me eliminate lead screw whip.

The X-axis will be set up much like the rockcliff design, except using .75" Thomson rails and Igus sleeve bearings.

I attached a couple preliminary CAD drawings to show the initial design. Let me hear some feed back.

[DonFrambach]

Have you considered a rack and pinion drive?

[prcdslnc13]

I have considered rack and pinion, but It seems like theres less chance of backlash in a chain drive if tension is kept on the chain then with a rack and pinion drive. Also I have a source to get the roller chain components for basically free, so that's persuaded me haha.

[DonFrambach]

get the roller chain components for basically free, so that's persuaded me haha.

That would persuade me too. Good luck and have fun with your build.

Don

[prcdslnc13]

Construction has officially started and is moving along swiftly. Some of my build plans have changed a bit, as they always do. But here are a few pictures. I have my torsion box for the base mostly built, the gantry bridge fully assembled, and lots of parts cut for the y and z axis. Its coming along slower then I thought,but coming and that's what counts. I even got to mock up the chain drive for the Y and drive it with a drill in place of the stepper motor. That was fun, made me feel like I have accomplished some thing.

Heres a link to a short vid of the Y axis too :banana:
[nomedia="http://www.youtube.com/watch?v=Az2K3HbYKpY"]YouTube - Eddi-P Y Axis travel[/nomedia]

[msimpson99]

Make sure you have lots of adjustment on your V bearings as it will wear the aluminium very quick until they are seated completly. Once seated they wont wear as much but they will wear.

[prcdslnc13]

Make sure you have lots of adjustment on your V bearings as it will wear the aluminium very quick until they are seated completly. Once seated they wont wear as much but they will wear.

I am following the thread you made about the festool router you used on your latest build. That machine is a work of art. What thickness angle did you use for that machine? I used 1/16th on this one because it sat into the v-groove nicer, but after pulling on it a bit Im wishing I would have gone with 1/8th.

as for adjustment, I gave myself 3/4" of play to make removing the board easier and for wear adjustment. I need to look at it and see if I need to give myself and more though. At this point remaking parts is super easy, so nows the time.

[msimpson99]

I used 1/8"

Just to seat the bearings you need about 1/16 on each side. Even more for long term wear. Another problem the aluminum has is that it does flex. I will probably eventualy replace all mine with steel. Its a simple problem to replace with out a tear down on my build. I simply loosen the vgroove so its nice and sloppy then remove the bolts holding the angle. I pull out one side and slip in a steel angle that has been drilled the same and reinsert the bolts.

Bottom line aluminum is ok for a first build and for learning but It does not work very well for a machine you dont want to constantly be tinkering with.

[prcdslnc13]

sounds good, and makes since. If I stick with v-grooves Ill probably replace with steel also. I will most likely replace them with THK Linear slides later on though.

[prcdslnc13]

Well another day off work and more progress has been completed!! I finished my Z axis slide today. complete with lead screw and all. When my motor couplers come later this week Ill make my motor mount for it too, but for now Ive left it off so when I get discouraged about this whole project, I can just go hook a drill to it and drive it back and forth lol!.

The z is comprised of Thomson 1/2" rails with Igus Sleeve bearings pressed into custom made sleeves. I then took HDPE and made blocks with my original CNC Router to hold the sleeve bearings into place and also to hold the rails and the actual carriage for the axis. A friend of mine made my bearing blocks and also helped me machine down the lead screw to fit in correctly.

Also Big news for the day, I now have THK HSR20 linear slides for both my X and Y axes! Super strong, Super Precise! Really stoked to get these on, but I bought the wrong size cap screw for them today so they will have to wait until later this week.

Heres the Pics!!!

[msimpson99]

Would love to see more info on the blocks and rails you chose. And lots of pics when you get them.


I have a big build in mind down the line and I Know I dont want to go with V bearings. Just too many issues.

[harryn]

Hi, would you mind posting some info on the chain drive parts and specs ?

[prcdslnc13]

Would love to see more info on the blocks and rails you chose. And lots of pics when you get them.


I have a big build in mind down the line and I Know I dont want to go with V bearings. Just too many issues.

The Blocks are THK HSR20
THK LM SYSTEM BEARING BLOCK HSR-20 HSR20HB1SS HSR20H - eBay (item 230538437565 end time Dec-13-10 13:29:06 PST)

Im not sure what the model number of the rails are. The only number I can find on them, theres no info on the internet about. Im assuming that a THK 20 rail will work. These are the same type of rails that commercial routers use, so Im assuming they will work for my puny (in comparison) guy.

As for the chain drive, Its #25 roller chain. Which means its a .25" pitch. Im using a 9 tooth sprocket to drive the machine, with works out to around 1 turn:2" travel (I think Im still figuring this chain stuff out). I got all these parts through McMaster Carr.

More pics to come tonight or tomorrow.

[harryn]

Hi, thanks for that info. I know with the belt drive components, I was surprised at how robust they had to be in order to deal with the forces involved, and the tolerances needed in order to make a low backlash setup.

All of the chain based systems I have ever used "stretched" with use, even with really nominal loads. (example, bike, garage door opener). I guess they must have been just barely enough for the load.

I looked at the mcmaster site, and it seems like you would need more like 40-2 chain to deal with the forces in a router, but I might be way off base here.

[prcdslnc13]

Im thinking the 25 should hold up fine. But ive been wrong before . Just gives an excuse for a rebuild right?. If I had to it again and didnt have the resources I have I would have gone rack and pinion though after seeing the cost of them. Time will tell.

Rail assembly tonight!!

[prcdslnc13]

Well I said in the earlier posts that I may toss out the v-bearings and angle for THK linear rails at some point. Remember that? Well some point was last night haha. I ended up with a set of rails for both the X and Y axes much sooner then planned. So I figured whats the point in messing with a tear down a month or two down the road when Im sick of looking at these. May as well do it now! So heres the run down of how they I set them up.

First the trucks at 2.5" wide and about 3" long minus the grease fittings. This worked out well as I planned for my Y carriage to be 7" wide. The grease fittings are accomadated as well because my rails are 1500mm long, this works out to 59"ish. I now have around 3/4" on either side of the rail so I can set up hard stops before the oil fittings crush, with no real axis loss. I spaced the rails so that they would be about an inch from the outter edge, this gave me enough clearance for my side boards on the bridge.

I set my current router up to cut 2.5" wide .125" deep slots across my Y axis board, and drill .375" holes for the chain drive mount about the bridge. This gave me the perfect area to mount my trucks inline and parallel. If you know anything about THK slides, there is absolutely no play and no room for error.

Knowing that I waited to mount my rails until the Y carriage was slid onto the rails. This allowed me to keep everything inline. I aligned the top rail to be square to the gantry and put a bolt on either side. Then I slide the carriage to one side of the track and C-clamped the rail in place. Then slid to the other side and again clamped in place. I drove it around for a few minutes to make sure everything was aligned then bolted the bottom down.

X-axis starts tonight!

[prcdslnc13]

Well after almost 5 days straight of working, and very little sleep, the router lives. My goal was to have it running by thanksgiving, and at 130am that day, I ran the splash page code from EMC2 with a sharpie in a makeshift holder. After all that though, the computer I was using to run it died . The mother board no longer recognizes hard drives. So Ive got to get that figured out. But all in all the build has gone great.

I wont go into super detail about the build process, mostly because I dont remember alot of it haha, Ill hit some of the lighter points, and theres lots of pictures.

starting from the beginning of the build weekend:

I had the gantry assembled as you saw in the last post. I was going to start the X axis, But I decided to got with a top down approach. I built up the z axis basically as an attachment to the Y carraiage. This gave me some flexibility later if I decide I want to change my rail system. Once I attached the z to the Y I started building the machine base. Thats the 2x4 monstrosity you see. Framing clamps are a must for this part.

Once that was together I screwed the torsion box directly to the crossmembers. At this point you could park a small car on the base.

I then mounted my uprights to athe gantry with T-nuts and stood the whole thing up and mounted them to the base.

For the X I handled the rails pretty much the same whay I did the Y rails, except I had to raise them, so I mounted them to MDF and then mounted the MDF to the table.

THe Y axis is chain driven and moves around 1200 IPM. Its way faster then the X can ever hope to be, and I still have some kinks to work out. but right now im seeing 80-90 IPM. I had to use a belt drive to hide the motor because of space constraints. This works out though because when I get the correct pulleys Ill be doing a 4:1 ratio, so that will speed my screw up a bit I hope.

Anyway heres the pics comment and question away!!

[prcdslnc13]

pics

[prcdslnc13]

Just ran my first part. Its the z-axis motor mount thats currently on the machine. It was an existing program that I ran on my smaller machine last time. Guess which one was more awesome .

All in all the machine did pretty good. The belt drive is proving to be a huge head ache. I actually cut that motor mount so I can rig up a direct drive system for the x-axis motor. The pulleys are enough that my stepper has trouble getting into its torque range, therefore doesnt want to get things moving very well. So I'd like to see what I can run like directly. What are you guys getting speedwise with a 400oz in stepper and a 1/2-10 acme screw?

[prcdslnc13]

BTW I ran all this using a bootable flash drive with the Ubuntu 10.04 live cd on it from linuxcnc.org. Not ideal but its great to know that if a computer bombs out but can still boot, this works haha.