linear rails for a plasma?

[landmark]

I've put together a design for a plasma and I'm trying to decide on if I should go with Hiwin 15mm rails or cold rolled flat bar and a bearing set up built by cncrouterparts.com. My cost between the two is comparable, only about a $40 difference for the X and y. I have seen lots of lower end machines use the bearing methoud and lots of higher end machines use linear rails. My design requires my rails to be on the top of each axis due to rack and pinions on the side.

Question 1: Will I encounter lots of problems with plasma gunk messing up my rails? I have heard of the flat bar systems having trouble with stuff getting on the rails and causing the steppers to skip. I also have noticed that torchmate uses linear rail on the front of their gantrys, which seems like it would be in a spot to get alot of junk on it. I was thinking that since my rails will be mounted on the top of my gantry and sides they may be a bit more protected.

Question 2: Am I a fool if I try to use one bearing block on either side of my gantry? My gantry is 60" long and has dual drive rack and pinion. The rails I planned on using where hiwin 15mm. Should I be looking to rely solely on the steppers to maintain squareness or should I do two blocks on either side to add more ridgity.

Thanks alot for any advice you can give.

[millman52]

I've put together a design for a plasma and I'm trying to decide on if I should go with Hiwin 15mm rails or cold rolled flat bar and a bearing set up built by cncrouterparts.com. My cost between the two is comparable, only about a $40 difference for the X and y. I have seen lots of lower end machines use the bearing method and lots of higher end machines use linear rails. My design requires my rails to be on the top of each axis due to rack and pinions on the side.

Question 1: Will I encounter lots of problems with plasma gunk messing up my rails? I have heard of the flat bar systems having trouble with stuff getting on the rails and causing the steppers to skip. I also have noticed that torchmate uses linear rail on the front of their gantrys, which seems like it would be in a spot to get alot of junk on it. I was thinking that since my rails will be mounted on the top of my gantry and sides they may be a bit more protected.

Question 2: Am I a fool if I try to use one bearing block on either side of my gantry? My gantry is 60" long and has dual drive rack and pinion. The rails I planned on using where hiwin 15mm. Should I be looking to rely solely on the steppers to maintain squareness or should I do two blocks on either side to add more ridgity.

Thanks alot for any advice you can give.

I have a home build with CR flat bar on 1 side of the long axis. You do have to keep junk larger than dust the machine creates brushed off the rail. All I have to do is run a bench brush over them prior to cutting a sheet. The only time I have ever had a problem was forgetting to dust it off after removing cut pieces & slag, dross whatever you want to call it has landed on the flat bar. Never has sparks or spray from cutting caused a problem.

I think you most definitely need more than (1) 15mm bearing cassette per side of table. For that matter I really don't think 15mm rail is robust enough for the job. Your steppers will hold your gantry square. You will most likely have some deflection or spring in your gantry even with a linear rail on each side with 2 bearings per side.

When the pinions are disengaged from the racks, it is very wiggly.

I am of the opinion for a plasma table all you need on your long axis is V rail & bearings on top & possibly a standard ball bearing or cam follower bearing underneath somewhere to prevent racking on sudden direction changes.

On a 60" gantry I would want a minimum of 20-25MM profiled linear rail for that axis.

The bearing sets from CNC router parts look like a very nice setup. I think I would want 2 of them per side.

[millman52]

I used a home made rail that works the same as V rail & bearings. I also used a flat rail & home made bearing truck not even close as nice as cncrouterparts.

Started building new 5 X 10 table today

Go here & look at posts 1, 8, 34, 37, & 46. What I done here costs almost nothing & has worked without exception. It is however time intensive to build. When I build again I will use V rail in place of the round bar. I'll use the same setup on the side with flat bar except I'll probably put it on the bottom side of the box tubing to get it out of the way when loading/unloading the table.

This table has over 2 years of almost daily usage on it. I feel the design is very sound & will hold up for many more years. I just need a longer bed table.


I have nothing but gravity holding the bearings to the rail on the round bar side. The other side has bearings on top & underneath the flat bar to prevent any racking under rapid direction changes. My table rapids at apx. 475 IPM & has never offered to rattle around on the rails.

[scrambled]

I am using linear rails on my set-up. I went with 25 and 35 mm rails. The 35mm are for the x axis and they are 16 feet long

Steve

[landmark]

Thanks for that feedback millman. Well at this point I have priced out the cost of two my options of going with bearings or linear rails and I'm coming up with $175 difference if I go with 20mm slides and two blocks on each side of my gantry as opposed to going with cncrouterparts stuff (using two carriages on each side of the gantry).

I am looking to build this for resale. I think I can build a better machine than the competition including things like z axis, floating head, linear rails, easy construction, bent slat design, and cable carriers all standard and still come in under their prices.
For a price differance of $175 on a 4x4 machine do you think it's worth the selling point of linear rails. Or will potential issues with debris be to much of an issue for the rails.
Thanks

[millman52]

Thanks for that feedback millman. Well at this point I have priced out the cost of two my options of going with bearings or linear rails and I'm coming up with $175 difference if I go with 20mm slides and two blocks on each side of my gantry as opposed to going with cncrouterparts stuff (using two carriages on each side of the gantry).

I am looking to build this for resale. I think I can build a better machine than the competition including things like z axis, floating head, linear rails, easy construction, bent slat design, and cable carriers all standard and still come in under their prices.
For a price differance of $175 on a 4x4 machine do you think it's worth the selling point of linear rails. Or will potential issues with debris be to much of an issue for the rails.
Thanks

I think linear rails will help sell the table to most people. I don't like them for plasma for the simple reason plasma cutting is a nasty process that creates mountains of black gritty dust. Now you are going to combine that with rails that need greased. I don't care how well they are sealed eventually grung is going to get in there. Need I say more. I do like linear rail on the gantry but I like Parker-Origa rial that DOES NOT use recirculating ball type casettes. The parker rail uses sealed needle bearing rollers & the preload can be adjusted as wear develops. Catch there is IT AINT CHEAP. Take a good look at Torchmates higher end gantrys. Parker or something similar is what they are using.

Trust me I am not trying to push anything else on you. The V rails & bearings run dry & are self cleaning because of the wiping action the bearings create as they are rolling along the rail. They are hardened & resist wear very well. Not only that, if wear developes, the gantry settles straight down & the THC will compensate. It's how straight & square you build the rails/gantry & as near 00.00 backlash you can design & build your drives that equate to accuracy. Also the simpler you can keep to repair the better too.

[jimcolt]

There are thousands of industrial high definition class (read: over $100k) with linear rails and greasable recirculating bearings. These bearings use rubber wiper type seals......and I have never heard of one failing due to dirt and grime. Some have been in service for 15 to 18 years running 3 shifts a day.

Jim Colt

[millman52]

There are thousands of industrial high definition class (read: over $100k) with linear rails and greasable recirculating bearings. These bearings use rubber wiper type seals......and I have never heard of one failing due to dirt and grime. Some have been in service for 15 to 18 years running 3 shifts a day.

Jim Colt

I have no doubt Jim that you are correct. At the same time I'm also confident that much more attenton is paid to the seal/wiper combination on the bearings & most probably have some sort of shielding of the rails to boot.
most probably bolt in from the bottom too which gives a proper sealing surface void of screw holes.

I'll admit I don't know what the big guys do I haven't seen that much of it.

I'd almost bet they arent the garden variety, off the shelf hiwin etc. rail & casette.

I know I have had contamination problems with IKO & yes they were sealed carriers. Just speaking from my limited experience.

[jimcolt]

Most of the recirc bearing and rail manufacturers produce plugs/and or stainless covers that go over the mounting screw holes. These improve the integrity of the seals. The price of these linear bearing has come down so much in the last 10 years that it seems to be the way to go...even with budget machines. If you can save money in labor...and produce a machine with better tracking and motion....then often it is worth spending a bit more for the components. I see a lot of machine builders wrestle with using flat bar and bearings to guide machines......getting it straight over long distances can be done, but it is difficult!

Jim

[millman52]

Take a look at this rail http://www.parkeroriga.com/pdf_catal...ear_Guides.pdf

This is what I have opted to use to replace a bad rail on my gantry. When speaking with their engineering dept a combination seal scraper/wiper is used on the cassette for environments like plasma tables. The cassettes are also have permanent lubrication.

[landmark]

Thanks for the advice guys. I think we'll give linear rails a try. After priceing all the options hiwin rails still comes out on top. I'll take your advice millman and go with the 20mm. Hopefully extra wipers should do the trick.

[millman52]

Like I said earlier I think profiled linear rail is a very good selling point. Jim Colt really is the plasma machine expert on the Zone. My opinions are based partly on having a 15mm rail & bearings fail on my gantry.

Most likely a combination of things, probably not really heavy enough for application, seals on the bearing carriers were not that good even though the bearings were new when installed. No caps on the bolt holes.

Be sure when you order to request "caps" to fill the tops of the bolt holes. They are little push in plastic filler caps to keep dust/grit from collecting in the recessed holes. They don't cost much & in my opinion should come with every new rail purchased.

You are right in that they just aren't that much more expensive. Also take it from a Machinist & fabricator the profiled rail is much easier to get lined up straight than most other methods. & the bigger it is the better at least to a point.

When you get started with the build please begin a build log & post plenty of pictures. You'll get lots of help & others opinions.