[jzurek]

Thanks to everyone for your help so far. This is my basic design. Overall footprint will be 63" x 48". Please take a look at what I've done so far and offer comments and potential problems.

1/2"-10 ACME lead screws
20mm Glacern linear bearings on X and Y
SRS25M THK linear bearings on Z

8020 sizes:
1515 and 1530

Z mounting plates 1/2" thick 6061 Aluminum

I look forward to seeing what you think.

[DonFrambach]

For my router, I thought about using Glacern SB-20 rails as you have drawn them on my gantry axis but decided against it because I was concerned that the fully supported rails placed as you have drawn them would force the carriages to be oriented supoptimally for left to right cuts. If you are cutting right to left, the bottom carriages would be pushed down against the rails (optimal). On the other hand, if you cut left to right, the bottom carriages would be pulled out of the rails (sub-optimal). I believe that the supported SB-20 rails are designed to take high side and down forces but not up forces. To get around this problem, I have seen designs where one rail was placed on the bottom of the gantry and the other rail was placed on the front. That construction seemed a little complicated for me. I have also seen designs where unsupported rails were used but those rails themselves can flex. That's why I decided to use a steel plate and carriages from CNCRouterParts.com for my gantry axis.

Just want to add an addendum. While it would theoretically be great if one rail could be placed on the bottom of your gantry and the other on the top, it would be extremely difficult to make them exactly parallel so binding would be a real problem.

[DonFrambach]

Sorry to be finding fault, but your Z axis will not give you the 12" of travel that you want. In order to do that, you should reverse the coupling so that the router is mounted where you have the Z axis rails and the Z axis trucks are mounted on a plate that is attached to your gantry carriages. I did that on my router in order to gain stiffness rather than more travel but it is required if you want 12" of travel.

Oops! Just realized that it is someone else who is building a router with 12" of Z axis travel. http://www.cnczone.com/forums/diy-cn...ce_please.html

But you may want to consider the suggestion anyway.

[DonFrambach]

Final thought and I'll shut up for the night. You'll want to use 5 start 1/2 x 10 ACME lead screws for your X and Y axes. Single start will probably be good for your Z axis.

[jzurek]

Don,

You are not pointing out faults... that is the purpose of me posting this now rather than during the actual build. You are simply increasing CAD time and saving me from scrap and aggravation later.

A.) I mounted the rails this way as to avoid hanging the bottom bearing block assembly with weight towards the open end. I had given no thought that the operation of the table would in fact create the same condition I was trying to avoid. Wouldn't having a rail on the bottom cause a problem? I do not want to use unsupported rail. I'll look into the rails you mentioned.

B.) I am looking for quite a bit of Z travel because the machine will have a 4th axis that I plan on being able to turn up to 6" spindles. I am a little confused by what you are saying. I'll have to read it again and think about it.

That said, thank you very much for the constructive criticism. It is very much appreciated.

Jeremy

One other comment... I would love to begin with 5-start ACME but considering I was originally planning on making the machine out of plywood my costs are already much higher than I originally planned. I plan on using the single start for now and once the machine is running and my credit card has cooled off swapping out to multiple starts later. I can deal with 40ipm travel for now.

[DonFrambach]

Here are some pictures from my router build, http://www.cnczone.com/forums/diy-cn...ry_router.html, that show what I mean by mounting the bearings back to back. The first picture shows the mount as I originally planned and is similiar to your current plan. The second two pictures show what I believe is a better mount that is much stiffer because it brings the bearings closer to the spindle and allows for much larger effective Z axis movement.

[skipper_52]

Back to the drawing board eh Jer? His point is well taken, something both of us overlooked. This forum has been great helping me build my machine and now yours.

Dad

[jzurek]

This is my first stab at the redesign. I see the problem you were talking about with the Z. I will probably tie the 8020 on the top and bottom together on the backside as well. New thoughts and problems?

Jeremy

[skipper_52]

Get to work

[jzurek]

I had today off. Where were you?

[jzurek]

So here is my next dilemma, is there a benefit to using these bearing assemblies on my x-axis rather than the open linear style bearings? I could build my x axis for cheaper. What is the accuracy of these bearings when they are compared to linear bearings?

Something like the attached pic. Has anyone had experience using these this way? Good, bad, problematic... feedback is appreciated.

[jzurek]

I've decided to go with the CNCROUTERPARTS.COM bearing assemblies. My question is, should I use two per x-rail or can I get away with one on a 42" gantry? Anyone?

[DonFrambach]

My question is, should I use two per x-rail or can I get away with one on a 42" gantry? Anyone?

I don't know but I would ask Ahren at CNCRouterParts.com. The advice he has left for others on this forum seems to me to be very good.

[tkubic]

4 for the x-axis 2 for y-axis 2 for z-axis.

total = 8

You need to constrain your axis so they don't lift or fall down, they only ride along a cold rolled steel rail.

Accuracy: assuming you put enough preload on them to negate any backlash They can only be as accurate as the rail they sit on. Which actually can be somewhat of a pain to find good ones.

I've seen really nasty picks of "warped" rails from online stores, mine when placed side by side revealed a ~.01" gap in a couple places over 60".

[jzurek]

.01" is quite a bit. I'm starting to wonder if this is the right way to go. How happy have you been using this setup? Thanks for confirming my suspicion that I need 4 for the X-axis.

[DonFrambach]

I only used short pieces of steel for my small router. One 7" wide and 23" long and one 4" wide and 10" long. They were as flat as my 8020 extrusions and easily bolted place. I have seen pictures of people getting steel plates with dinged edges. Mine arrived in perfect condition and seemed to be straight but I did not have a precise way to test for that.

The Glacern SB20 rails are great. Have you considered using CNCRouterParts.com carriages for your Y and Z axes and Glacern rails for your Y? That's what I did and I'm real happy with my router (at least so far).

[jzurek]

Don,

This build was originally going to be a Solsylva made out of baltic birch plywood. But then quickly got away from me. The first change was to use Glacern linear bearings on X and Y. But then I changed to 8020 and you had pointed out the problem with my y-axis, which BTW I do very much appreciate. So then I changed my Y bearings to bearing trucks from CNCROUTERPARTS.com With that change, I started looking at using them for my X-axis as well.

Now I'm second guessing myself and thinking that the Glacern bearings on X are really a better choice. With (4) bearing blocks from CNC and 4 flat plates ~60" long, it will probably be cheaper and more accurate for me to use the Glacern on X. With the bearings mounted with the open end down, I'm concerned that the bearings will still be in a suboptimal position however, with 4 of them and the weight of the gantry working against the downward force of the Z, I think I'll be okay.

My dad and I are building a replacement machine for his Solsylva that is almost identical to this new design for me. He will be using the cncrouterparts.com bearing trucks on his Z. Mine will be THK as I scored a good deal on SRS25 bearings and rail. But who knows, that may change as well.

I really appreciate you following the thread and offering comments. I'm shocked that I haven't seen anything from some of the other common contributors. The idea is to get this build 95% right before we start cutting aluminum.

[jzurek]

I have my control box mostly together. Here are pics so far.

Jeremy

[jzurek]

Well it's official, I fried one channel of my 4 channel board. I sent it back to Xylotex for replacement, luckily it is still uner the 90 day warranty period. In the meantime, I have gotten my Probotix rotary axis working I can't wait to get the panel back together and put on the shelf waiting patiently for the CNC to come join it in the basement.

I still have no clue how it happened. I had all my voltages set properly, did not disconnect any motor wiring while it was powered. It was working and then just quit. I hope this doesn't happen again. Also I've ordered my buffer card from CNC4PC to get my spindle relay working. My P4 does not supply enough power to the parallel port to throw the relay.

[jzurek]

Jeff sent the replacement Xylotex 4-Axis board to me. I opened the box last night. Hopefully tonight I'll have some time to install it on my subpanel and set my voltages. I don't think I'll be able to play with bumping the axis until this weekend. It's a lot of work to reinstall my subpanel in the enclosure.

I also ordered a buffer board from CNC4PC to bring my power up on the parallel port. The on-board parallel just didn't have enough oomph to pull in my spindle relay. Can't wait to start playing.