[ger21]

If you can build a machine using skate bearings, and get the whole thing rigid enough to bind from slight misalignment, I think you've moved beyond the capabilities of the cheap bearings. Bellevilles would be totally unecessary for a wood machine, but I guess they might help out with a metal frame machine.

I would 2nd having some mechinism to accomidate variations in tolerance. In a wood or MDF machine their is enough give or spring to roll over a tight spot. But the more ridgid you make it the more spot on it has to be, throw in temperature variations and a 100lb preload could change to a 500lb preload.
Including a handful of bellville washers in the assembly would maintain a resonable preload and allow the machine to roll past a tight spot wihout jamming and stalling. They have pretty wide range of sizes and you could put a dozen or two in the assembly without incurring much extra cost . I just got some 1/2" ones for acme scew preloading from MSC they were real resonable.
Barry

[ger21]

It's a 3-1/2 year project, but it's almost done. But it'll probably be another 6 months until I can find the time to finish it.
http://www.cnczone.com/forums/showthread.php?t=1356

[Oldmanandhistoy]

It's a 3-1/2 year project, but it's almost done. But it'll probably be another 6 months until I can find the time to finish it.
http://www.cnczone.com/forums/showthread.php?t=1356

I have had a flick through your machine thread (nice work btw) ;to be honest I only looked at the picture and never saw the bottom of your gantry. Just a quick question did you just use two lengths of all thread under the gantry?

John

P.S.

I will go back and take more time to read some of the posts so if the information is there never mind replying.

[ger21]

Yes, just 2 pieces.

[ger21]

John, ideally I'd like to get away from the threaded rods and suspended table. The trick is coming up with a compact design that will hold in all 4 directions. Most of what I've seen in this thread is more complex than I'd like.

[Oldmanandhistoy]

John, ideally I'd like to get away from the threaded rods and suspended table. The trick is coming up with a compact design that will hold in all 4 directions. Most of what I've seen in this thread is more complex than I'd like.

This seems like the Holy Grail to me also and I have been giving it some thought. The best I can come up with so far is to use twin rails with that G arrangement we discussed in the early posts on the bottom rail.

Still working on it.

John

[mike hide]

I think Joe and others have proved that even with a small contact area of a circle on a circle those little skate bearings will carry a pretty good load.
If they have full width contact it should be much greater.
I have been wrestling with how many is to many bearing maybe Ger or one of the other uber posters may be able to shed some light on when a bearing is just a hinderance not a help.

Talking about reducing contact loads ,some time ago GER suggested using two bearings on each shaft [bolt] . seems oldmans machine could benefit from this . This should have a better load distribution and in turn about halve the local loading . all it takes is an additional bearing and a spacer washer there apears to be enough space to accomplish this ...mjh

[Oldmanandhistoy]

John, ideally I'd like to get away from the threaded rods and suspended table. The trick is coming up with a compact design that will hold in all 4 directions. Most of what I've seen in this thread is more complex than I'd like.

Would you believe it I have just had a brain wave 2.00 a.m. not bad. I have done a quick sketch on paper and I think it might just work. It’s too late for me to do anything with it now but will draw it up tomorrow if I get the time and post it here for your opinions.
I’ll give you a clue; square tube rail turned 45 degrees to how I have it on my machine now. Fixed to side of the machine base with a stand off of some description. Two pieces of angle with bearings as you have them in your first post turned 45 degrees mounted to the gantry side for one to ride on top and one on the bottom.

John

Bet it keeps me awake now (nuts)

[Oldmanandhistoy]

Talking about reducing contact loads ,some time ago GER suggested using two bearings on each shaft [bolt] . seems oldmans machine could benefit from this . This should have a better load distribution and in turn about halve the local loading . all it takes is an additional bearing and a spacer washer there apears to be enough space to accomplish this ...mjh

Would need a very firm fixing method for the bearings; angle iron would be stiff enough with a good fixing method onto the gantry sides? A lot of preload and the cantilever effect may lift one of the bearings off of the rail?

What do you think?

John

[Oldmanandhistoy]

Would you believe it I have just had a brain wave 2.00 a.m. not bad. I have done a quick sketch on paper and I think it might just work. It’s too late for me to do anything with it now but will draw it up tomorrow if I get the time and post it here for your opinions.
I’ll give you a clue; square tube rail turned 45 degrees to how I have it on my machine now. Fixed to side of the machine base with a stand off of some description. Two pieces of angle with bearings as you have them in your first post turned 45 degrees mounted to the gantry side for one to ride on top and one on the bottom.

John

Bet it keeps me awake now (nuts)

I knew it would keep me awake; but I am positive it will work as long as the fixing method for the rail ( U channel for the stand offs btw) and angle is ridged enough. The bearings would be axially loaded but with twin bearing on the outer side of the rail (full contact) and just a single bearing on the inner side of the rail I would think it will work just fine.

John

[Oldmanandhistoy]

I knew it would keep me awake; but I am positive it will work as long as the fixing method for the rail ( U channel for the stand offs btw) and angle is ridged enough. The bearings would be axially loaded but with twin bearing on the outer side of the rail (full contact) and just a single bearing on the inner side of the rail I would think it will work just fine.

John

I have attached a quick drawing of what I was rambling on about last night.

BLUE: square steel tube.
GREEN: Angle (iron or aluminium)
MAGENTA: Bearing spacers
YELLOW: skate bearings
RED: M8 bolts and nuts
CYAN: M8 washers
WHITE: U channel and machine base side. I have drawn the U channel at about 0.75” but do not have spec’s so may need to be some other standard size. If U channel is no good then an alternative rail stand off will be required. I have my doubts about using U channel because of alignment issues and would probably go with an alternative method. I haven’t added the gantry sides so a simple fixing method needs to be found; but I do not see a problem here.
I have not drawn all the fixing bolts as this would have confused things but obviously two more are needed in the picture. If more explanation is needed please ask and I will do my best.

Maybe ger21 if he sees this as being a possible solution to the four sided bearing method we have been looking for could draw it up 3D if he has the time.

I have no more time now so you will have to take it as is for now.

What do you think?

John

[joecnc2006]

wouldn't this lead to twisting or rotating of the sq. steel?

[Oldmanandhistoy]

wouldn't this lead to twisting or rotating of the sq. steel?

As in moving in the U channel? That is why I said I would prefer a different stand off method.

It would be very easy to make a hardwood stand off with a 90 degree V cutter.

John

[spalm]

John, now we are back to many parts and axial loading. It seems a better approach to that would be as Mike did in his retrofit:

http://www.cnczone.com/forums/showpo...2&postcount=92

Thinking about this, how about running flat strap iron on the bottom of this rail instead. Then rigid mounting the top angle/bearing assembly and using eccentrics on the bottom bearings for preload? This would be self centering, no floating adjustment plate, and provide both horizontal and vertical attachment. No undercarriage box and floating table are needed if twin screws are used. The rail could be split into two or a piece of square channel used on the bottom if top/bottom parallel needs to be adjusted. (To cure axial loading, just use a V-bearing on top.)

This is essentially what I did on may last machine and what Benny and a few of the Australians did. We ran V-bearings on the top of large angle iron and standard bearings on the flat bottom. I went down and studied my machine last night. My earlier posts did not give the concept enough credit. The gantry with no under carriage is extremely stiff. I bear hugged it and I can not move it in any direction. What this means though is that absolutely no misalignment is allowed or it will bind. Both rails and both screws must be parallel in all directions (redundant). But I guess this is a good thing. Maybe only one V-bearing could be used on the top to save money if you believe in the triangle thing.

Steve

[Oldmanandhistoy]

John, now we are back to many parts and axial loading. It seems a better approach to that would be as Mike did in his retrofit:

http://www.cnczone.com/forums/showpo...2&postcount=92

I should have looked more closely at his machine; as you say it has already been done and is a better method than I have drawn. Thanks for the heads up, I just did not study his machine. Sorry for adding more confusion to this thread; I will go and do some thing more constructive now.

John

[spalm]

Hey Oldman, keep your head up!

My brain just won’t let go. This is why I had to quit homebuilt CNC for a while, it just consumes me. It is such an interesting 3D puzzle.

OK, how about this: (Probably on the Zone here somewhere else, but heh.) We want to lock the gantry in all directions but can only use radial bearings. Use two rails, one for horizontal and one for vertical. Use the square channel rail without the horizontal bearings, or some version of it that will pass the Zone’s Gods for the vertical attachment. Now add another rail to the top of the bed. Add another bearing truck arrangement (which again passes the aforementioned version control) that pinches the left and right sides of this top rail. This will do the horizontal attachment. Eccentrics could be used to keep out threaded rod and three bearing trucks to reduce parts counts (or not).

Steve

[Oldmanandhistoy]

Hey Oldman, keep your head up!

My brain just won’t let go. This is why I had to quit homebuilt CNC for a while, it just consumes me. It is such an interesting 3D puzzle.

OK, how about this: (Probably on the Zone here somewhere else, but heh.) We want to lock the gantry in all directions but can only use radial bearings. Use two rails, one for horizontal and one for vertical. Use the square channel rail without the horizontal bearings, or some version of it that will pass the Zone’s Gods for the vertical attachment. Now add another rail to the top of the bed. Add another bearing truck arrangement (which again passes the aforementioned version control) that pinches the left and right sides of this top rail. This will do the horizontal attachment. Eccentrics could be used to keep out threaded rod and three bearing trucks to reduce parts counts (or not).

Steve

As you say many possibilities have probably been done some where on the Zone. What would be helpful to me and I would guess quite a few other members would be if anyone has a design which is an alternative to round tube systems (keeping to the subject of this thread) or has seen a design else where. They could post a link or picture here with a brief word on positives and may be negatives of that design. I am sure there will be quite a few people pass this way that would benefit from a number of different designs in one place to scrutinise before going off to design a system that could have been improved upon had they seen a particular design alternative.

I will start things off with a link to this thread http://www.cnczone.com/forums/showthread.php?t=35936. Started by the_extreme; he uses hex rail and I particularly like the idea for a Z axis. It’s a nice clean simple design and I would think quite rigid. Would be interested to know what other may think about this one?

John

EDIT: btw spalm had a look at your build thread; nice job

[Kipper]

It's a terrible thing to have an idea in your head...Makes it hurt I think I'm about done thinking for now (brain hurting and it's time for sleep) I'm going to see if I can get a half scale version of this made in the next couple of weeks and then hammer it to see how well it holds up! Thoughts anyone?

[barum]

See my design. No wood, just metal
Only cheap parts easy to find. That is M6x1, 13x13 steel, 40x20 aluminium and bearings (36 pieces total).
Nothing special but works fine



Bojan

[Oldmanandhistoy]

No wood, just metal
Only cheap parts easy to find. That is M6x1, 13x13 steel, 40x20 aluminium and bearings (36 pieces total).
Nothing special but works fine



Bojan

Looks very interesting

First question; what is the wall thickness of the steel tubes and have you noticed any distortion?

How do/did you mount this arrangement to the machine and is it for a particular axis?

How are you attaching the rails?

Nice drawing btw what did you use in way of CAD?

Thanks for posting,

John

EDIT: Just noticed it is your first post; welcome to the Zone