All metal Z-axis design useing skate bearings and cold rolled steel

[FandZ]

Hi all, I'm getting closer to starting a build for my next machine. On my last build, my Z axis really caught me by surprise so this time I'm starting with my Z axis.

If you look at the pictures below, All the dark metal is cold rolled steel. The roller assemblies would be 1/2 in. x 1/2 in. and the rail would be 1.5x1.5 cold rolled steel. The aluminum would be .5 inches thick except for the anti backlash nut plate and the stepper mounts. Total Z travel would be between 5 and 6 inches.

Besides the width of the bolts shaft, none of the bolts are to any exact specs but they are close. I may go with allen bolts but I haven't decided. As you can tell there will be a lot of drilling and tapping at hand. Oh and I also left out the spacers for the bearings and lock washers. They will not be rolling on the very edge.

As far building it, my local metal supply shop will be cutting the metal to length and my current cnc would be used to mark the metal for drilling on my drill press to get the tight tolerances I'm looking for.

I'm still working on it but if anyone has any concerns or suggestions on this design I'd be glad to hear them. The only concern I really have is how the .5x.5 roller assembles extend 3 inches after the bearings for the spindle mount. My goal is to comfortably work in aluminum.

[CarveOne]

I suppose that 1.5" x 1.5" steel rail won't be bending anytime soon.

It's an interesting design concept. I would recommend changing the steel spacer block behind the router mounts to aluminum to lighten the moving load on the stepper by that much. I think there would be no strength advantage in it being steel for that application.

The four steel bearing bars may be strong enough if made of aluminum, but it's probably better to overbuild those than to underbuild them. .5" x .5" aluminum might be a little marginal here.

Do you plan to place the Y axis lead nut behind the vertical aluminum plate?

CarveOne

[Regnar]

The design looks good and simple to construct. What could make it easier is if you shortend the 1.5 square cold rolled steel and extended the 2 aluminum pieces that have the bearing attached to them to go over the steel stock. I think you will find that it might be hard to drill 2 holes straight through 1.5 inches of steel to meet up with 2 threaded holes in aluminum. Drill and thread the steel on the ends and drill the holes through the aluminum. This should also help in keeping everything square if the steel is cut square.

I hope you plan the rest of the machine to be beefy. This Z axis is going to weigh a pretty considerable amount.

Also for the stepper mount you might find it easier to make these out of square or rectangular aluminum tubing. This way you can bolt down rather than up. If you make the mounting holes a little larger you can move the stepper motor around if everything doesnt line up as nice. Right now you have to be dead on.

[CarveOne]

Originally Posted by Regnar The design looks good and simple to construct. What could make it easier is if you shortend the 1.5 square cold rolled steel and extended the 2 aluminum pieces that have the bearing attached to them to go over the steel stock. I think you will find that it might be hard to drill 2 holes straight through 1.5 inches of steel to meet up with 2 threaded holes in aluminum. Drill and thread the steel on the ends and drill the holes through the aluminum. This should also help in keeping everything square if the steel is cut square. I hope you plan the rest of the machine to be beefy. This Z axis is going to weigh a pretty considerable amount.

The solid steel bar will be very heavy, but it is at least not a part that the stepper has to lift. I was going to suggest making that rail out of 1.5" x 1.5" x .120" steel box tube to save on weight, but I went out to the work shop and looked at the 1x2 and 2x2 box tubes I have and though 5/16" wide bearings would roll at the radiused corners ok, there are little ridges that make it dimensionally problematic. The ridges could be lightly oil-stoned off but I doubt that anyone would be happy with the results. The ridges are left during manufacturing by swaging the tubing to size.

CarveOne

[Regnar]

Just another thought, if you were to mount the leadscrew off to the left or right of your 1.5 square bar you should be able to bring every thing in closer to the y axis so that the weight doesnt stick out as much. Again just suggestions dont know what the rest of the system looks like or what else you have in mind.

CarveOne, I was also thinking he could do some lighting holes down the center of each side. Make half inch hole skip and inch and do another. I dont know how much it would help but I dont think it would hurt in anyway either.

Picture of all the ideals into one.

[CarveOne]

Originally Posted by Regnar -Snip- CarveOne, I was also thinking he could do some lighting holes down the center of each side. Make half inch hole skip and inch and do another. I dont know how much it would help but I dont think it would hurt in anyway either. Picture of all the ideals into one.

That will be one way to do it. Another is to drill a 1/2" hole (or 3/4" ?) into the top and bottom hole as far as a drill will go, centered in the ends of the bar.

If overall gantry weight is not an issue I would just leave it solid. On my 2nd build I avoided steel as much as I could in the sliding part of the Z assembly.


OOPS!! Forget the hole in the ends idea, I see bolts there.


CarveOne

[FandZ]

Hey guys, thanks so much for your suggestions. Just the kind of feedback I’m looking for.

I’m not too worried about weight so much, In fact, I’m aiming to have a heavier machine over all to reduce vibrations in the hopes of a better finish. I say heavy but I’m thinking it’ll end up weighing around 200 to 250. Most of that weight will be over the cutting table as I’m designing with the X axis suspended above the cutting table. Sort of parallel with the Z axis. I guess that is not so heavy really. Should be interesting. I would post the design but I’d hate for someone else to build something close to it before I have had the chance lol..

Originally Posted by Regnar What could make it easier is if you shortened the 1.5 square cold rolled steel and extended the 2 aluminum pieces that have the bearing attached to them to go over the steel stock. Also for the stepper mount you might find it easier to make these out of square or rectangular aluminum tubing. This way you can bolt down rather than up.

I see what you are saying. I originally designed it that way but the place doing the cutting gives a 1/16th of an inch plus or minus on cuts. The way I have it I’m using 3 inch wide bars of aluminum cut to length so I won’t have to worry if my steel bar is 1/16 too short or long. Hrmm but it would be easier to mount it with your way. I’ll post a picture of an idea.

I may just have to go with your idea on the stepper motor. I was planning on making the holes for the bearings that hold the acme rod bigger but it may be better to just have to adjust the motor than both of those.

Originally Posted by CarveOne I was going to suggest making that rail out of 1.5" x 1.5" x .120" steel box tube to save on weight, but I went out to the work shop and looked at the 1x2 and 2x2 box tubes I have and though 5/16" wide bearings would roll at the radiused corners ok, CarveOne

On my last machine I used 1x1 steel tubes for rails. It worked fine but the finish isn’t that great as you suggest and there are low spots where one bearing can be turned in place. Not good, I’m sure.

Originally Posted by Regnar Just another thought, if you were to mount the leads crew off to the left or right of your 1.5 square bar you should be able to bring everything in closer to the y axis so that the weight doesn’t stick out as much.

Hrmm.. I originally started with two 1.5 inch steel bars and an acme screw near the center. It saved a little over an inch but I decided it was a little too much..lol I’ll post a picture.

The suggestions to drill holes to reduce weight are great. I never thought of that. If my Y axis struggles I will do it for sure. For now I plan on leaving it solid. I’m wanting the weight.

Someone mentioned it may be hard to drill straight through the steel bar with accuracy. I was wondering about this. What do you think if I try it first and if the ends are off I drill a bigger hole through half of it on the side that mates with the aluminum shelf? Or maybe drill the bigger holes first and then only have to drill ¼ an inch precisely with a smaller drill bit on the other side?


Again. Thanks for the suggestions

[FandZ]

Idea and first design.



Now that I look at the big I dea it would further the distance of the rail. I think I'm just going to have to man up to save that half inch.

[CarveOne]

Originally Posted by FandZ - snip- Someone mentioned it may be hard to drill straight through the steel bar with accuracy. I was wondering about this. What do you think if I try it first and if the ends are off I drill a bigger hole through half of it on the side that mates with the aluminum shelf? Or maybe drill the bigger holes first and then only have to drill ¼ an inch precisely with a smaller drill bit on the other side? Again. Thanks for the suggestions

If you are talking about an end to end hole, the bar is probably too long for most 1/2" drills to reach deep enough to meet at the middle, and they are very likely to not be aligned. In this case it will not matter much, as it can't be seen anyway. Not meeting in the middle is no problem either. It could be finished with a boring bar in a lathe. Boring bars that fit a 1/2" hole are usually very limber.

Drilling crosswise holes should not be a problem if a sharp bit is used. A split point drill will stay on course better than a regular drill.

CarveOne

[FandZ]

Originally Posted by CarveOne Drilling crosswise holes should not be a problem if a sharp bit is used. A split point drill will stay on course better than a regular drill. CarveOne

It was the cross wise I was worried about. thanks for tip on the drill bit tip.That's what I'll get and do.

[Jason Marsha]

FandZ,

Not sure if my assemblies are from hot or cold rolled but I used 16mm (5/8") solid square bar and the holes for the bearing bolts had to be drilled halfway through from each side because the bar was not square. I also had to use a center punch to stop the wandering bit whether split point or regular.

Jason

[FandZ]

Originally Posted by Jason Marsha FandZ, Not sure if my assemblies are from hot or cold rolled but I used 16mm (5/8") solid square bar and the holes for the bearing bolts had to be drilled halfway through from each side because the bar was not square. I also had to use a center punch to stop the wandering bit whether split point or regular. Jason

Cold rolled is known for it close tolerances so it better be square or me and the shop will be having a talk lol... I was going to use my existing cnc machine as a high tech punch to mark my drill points. I may make some sort of tool to hold my punch and align it from the edges. On my last build I wish I would have made a punch holder because scribing lines and then punching didn't work out too great for me. I did a lot of redo's.