[hoarp001]

Hi Everyone,


I am planning a CNC router table with a 2 meter Y axis, and I am wondering what to use for the guide rails.

I have found this stuff,

http://uk.rs-online.com/web/search/s...duct&R=4885265


Which looks ideal but only in lengths of one meter.


It would be good to hear of any guide rail that is strong and smooth/precise and available in 2m long peices.



Thanks.

[jhowelb]

Igus rail is GOOD stuff.
http://www.cnczone.com/forums/showthread.php?t=88722

Used it on mine.

Try this site to find prices, etc then call for an order.
http://www.igus.com/show_dw.asp

[hoarp001]

Hi,

The machine I am planning is fairly heavy duty, and the gantry will be made from 5x1.5inch box section steel. This is so it is durable etc, but hopefuly will be capeable of cutting harder materials than just MDF.

I have designed it with the 80mm spacing drylin rail stuff on either side. I am just wondering if its strong enough.


We actually use this rail in film and tv, and put cameras on it. It makes a nice device to slide cameras side to side, which is how I know about it in the first place.

Aslong as you think its strong enough, and its available in 2m long peices, then it should be perfect.


Pete.

[jhowelb]

They will cut to measure. There are different sizes and the square rail will handle more weight than the round.

Drylin W is only one choice, they make even larger stuff. Take up the subject with their tech department.

I am hardly an authority on Igus and have no connection other than I am a happy customer.

Keep this thread going with pictures and comments on your progress!

Regards

[hoarp001]

Ok well since you asked.




You can see the sliders along the sides and on the gantry. The red thigns are bearings or leadscrew nuts. You can see a green thing through the 'glass' table which is the nut for the leadscrew on the Y axis.

Neat eh?


cant wait to get started.

[jhowelb]

Your design should be very easily achieved with "8020" type T slotted aluminum extrusions.

If I may offer one bit of constructive criticism, it appears that you might be getting ready to fall into a common pitfall for slide bearings. The distance between bearings front to back as compared to the width of the gantry and the moment of resistance seems extreme.

I believe this is going to result in some binding.

The distance between 1 and 2 needs to be half the distance from 1 to the lead screw (so I've been told) and the distance from 3 to 4 no more than twice the distance from 1 to 2.

My design does not meet this criteria but I compensated with a cable system without which the bearings may as well be welded to the rail.

Please don't get me wrong, I very much wish to give you encouragement, but a word of warning from one who invested much time and money in a failure and who learned the hard way can be invaluable.

[hoarp001]

Ok, well better i know the rules now, when the machine is just a drawing than after I start building it. I will re-jig all of this to fix it. Infact, I think I can fix it fairly easily.

I am reluctant to use the aluminium, this will be used as an industrial machine, and im not very good at welding aluminium. I would rather have a solid welded and powder coated structure than one made out of over sized Knex peices, even if it is strong, as I am sure it is.


Thanks for the advice, will add some bits to my design. Will reduce the Y travel though



Pete.

[hoarp001]

Hi Again,

I just re-read your post, and you say the distance between 1 and 2 needs to be half the distance between 1 (the bearing) and the leadscrew. This distacne is about 20cm (5inches roughly)

That can't be right?!

[jhowelb]

Unfortunately that is right.

If you look at my machine, the distance from 1 to 3 is 32" and the distance from 1 to 2 is 6". The lead screw is only two inches on one side but 34" on the other side. The cable system is attached directly to the slide bearing which makes the other measurements irrelevant.

The other "catch" is that from the cutting board to the cross piece of the bridge is 9" BUT the rails are 3" above the board making the 3 to 4 measurement 4" while the 1 to 2 measurement at 6" is even greater than required.

So, figure out how much clearance you HAVE to have and build only slightly more. make your 1 to 2 dimension half of that and then either use two lead screws (one on each side) or use the cable system. There is a thread on the forum dealing with just that. Lots of guys have had lots of grief over this item!!

Look here! http://www.cnczone.com/forums/showth...try+rock+solid

[hoarp001]

This still makes no sense, you say the distance between 1 and 2 (the width of the bearing slider, and in the case of the Igus stuff, this is the distance between the two slider vblocks) needs to be HALF the distance between the bearing (1 and 2) and lead screw.

The leadscrew is directly under this, about five inches. This would mean that using this rule, the guide rails only need to be 2.5 inches apart. This cant be right?


Did you mean that the 1-2 distance needs to be half the distance between 1&2 and the top leadscrew? If this is the case then I get what you mean.

I also dont understand what you mean by the 1-3 distance. When dealing purely with the Y axis, the width shouldn't matter, a machine twice as wide would present exactly the same challenges, apart from the extra weight of the parts.

I had been wondering since I had started drawing this that the bearings might bind and was considering widening this by adding a second igus carrage on either side. Doing this though either reduces my Y axis travel or means I have to extend the length of the cutting bed. Doing this means longer rail, longer screws etc.

I think all I would need to do to make this design work, is to add another igus carrage on either side to stop it binding....

[jhowelb]

I think we are getting tangled up in terminology. To simplify our discussion let's consider only the bottom most axis, whether you call that X or Y.

Even with the lead screw exactly in the center the machine will try to torque the slide bearings one way or the other. To counteract that force the distance between the bearings on the same rail (1 to 2) needs to be bigger.

Lets assume that the rails are 30" apart (1 to 3) then the lead screw is 15" from either rail. What was suggested to me is that the distance from fron to back (1 to 2) of the bearing arrangement should be 7.5" or more.

The height of the gantry bridge (3 to 4) will have a similar effect.

If what I'm saying still does not gell then you probably should take the subject up with Igus tech staff. They will be glad to discuss it with you on the phone.

[jhowelb]

Here is a picture of an actuating table I lifted from Igus' pages.

Notice how narrow 3 to 4 is compared to 1 to 2. The design is to eliminate torque around the center of the bearing.