3dprintforums logo

CNCzone Network:  RFQwork :: 3Dprintforums :: Welderzone :: Google+ :: Our Facebook :: Twitter :: SiteMap



Page 1 of 7 1234 ... LastLast
Results 1 to 12 of 78

Thread: DIY Linear Rails

  1. #1
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10

    DIY Linear Rails

    Ok, I know lots of people are building their own rails or rail systems in a variety of ways. I've worked out a couple ways of doing it myself, however in doing so I've come across some issues and questions.
    I'm planning to go one of two possible routes. First a couple points about my planned system.

    It's to be a Gantry style mill/router system for machining foam and some MDF only. The entire system will be composed of sqr or rect HSS [steel] sections. The foot print is fairly large and this is a medium which I'm comfortable with. The basic structure is two HSS rails running the length of the 'X' with smaller cross tubes connecting them [parrellel to the 'Y']. There is some conciderable weight to the whole setup, currently in my design the Gantry weigh's about 1200 lb's. The entire system is floor mounted to a concrete pad. Accuracy from my system optimally would be in the 1/64"- to 1/32" range, this is tight for a large system like this, and maybe I'm totally out to lunch on these numbers, but the closer I can keep to this, obviously the better.
    Basic dim's of my system are X=20', Y=10' and Z=~5'.

    Now the options:

    Route A:
    The typical angle iron rails, there will be four on the x axis and two on the y axis.[ two on either x rail and 1 on each of the two y rails] The Z axis will be composed of actual linear rails [ THK or the like].

    Route B:
    A second idea was to place a heavy 'T' rail, composed from 2 pc's of CRS,on top of the X rails. Then run several roller bearings on the top, side and a few on the bottom side also, to create a completly controlled linear travel. Each bearing would be adjustable via an eccentric bushing [ thats another post in this forum]. The same basic idea would be applied to the Y axis also.

    So whats my dilemma?

    Well with Route A, I'm concerned that there will be some warpage of the X rails while welding. I've got several small laser cut jigs designed to temporarily place the angle iron in its proper position for welding, it would then be stitch welded in many locations in an alternating pattern to help reduce heat shrinking and warpage. The possibility of heat distortion of the X rails could lead to a rail which either moves up and down along its length, or it will 'roll' along its length [ twist] and cause binding in that way.. or it could do both. There is a certain amount of warpage which can be taken out when the unit is floor mounted, however this is rather limited.
    So short answer is.. warpage and accuracy issues.

    Route B is a bit negative simply because of all the extra connections required to keep the 'truck' on the rail. There would need to be trucks on all four sides of the rails which all have to be finitely adjustable to make it work. There will also be the requirment for joining the main rails because CRS doesn't come in over 12' lengths [ that I've found anyway].Another issue is simply weight, this route's linear system will way heavier than route A. There will be less worry about warpage [ as in route A] however this route leads to many.. many more headaches. Mind you, if a person could get it working.. in the end it may be the better system.
    The short answer for this one, is cost, weight and complexity.

    Ok, so I wrote that whole book to simply ask the following. Has anyone done a system similar to either of these in this large of scale [ 8 or more feet long in any axis]?? If you have, which route did you take? Did you experiance any of these issues while traveling that route, and if so, what did you do to solve these issues? Did you do something similar, yet different?

    I know that I'm probably missing several more issues with both of these idea's [ if you see anything that would significantly impact these designs please speak up! ] However, either of these two designs will end up being many many dollars cheaper than going with a complete store bought linear rail system.


    JerryFlyGuy

    Similar Threads:
    Last edited by JerryFlyGuy; 01-20-2006 at 03:34 PM.


  2. #2
    Registered
    Join Date
    Dec 2005
    Location
    USA
    Posts
    19
    Downloads
    0
    Uploads
    0
    Rep Power
    0

    Another angle on the angle iron tracks.

    Hello,
    I have been thinking about an affordable reasonably accurate track system as well. One of the solutions I am considering is to take cold formed square stock and place the sections end to end rotated 45 degrees with machined supports made with a "V" top and a hole through the center to allow a bolt to come up through the flange on channel or I-Beam supports and thread into holes drilled and tapped approximately 50% of the diagonal of the square stock. This would allow one to place shim stock under the supports to compensate for the variances in the channel or I-beam supports. Additional support with a tapped hole would be placed under each junction of the square stock to insure alignment under load. Supports would need to be spaced such that the calculated deflection of the square stock with worst case load from one carrier would be minimal. If you plan on a rack and pinion drive with a spring or pnuematic preload mounted above this track on the opposite flange from the track you should be able to go with one track per side. I would think this size gantry would demand a rack and pinion and drive on both sides.
    For this large of a system it is definitely worth looking at cable drive for the x axis for the sake of economy. If this is done it will require the mounting of a second track inverted above the first one in place of the rack and pinions. You will want to design the v roller system for the upper track to have a spring or pnuematic preload system as well. The cables on each side can be driven from a common shaft and one motor. As long as the cables are pretensioned properly the positioning accuracy can be impressive after a short initial period of time where there will be a small amount of stretch until the cable "sets". You will need to machine drive pulleys for the cable that allow at least 5 complete wrapps of the cable around them winch fashion to make sure there is no slippage.
    If you are determined enough this system should be able to be shimmed in to an accuracy of a few thou at any given temp despite the large size. If you find something that looks better for the money let me know.



  3. #3
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Twp, MI....USA
    Posts
    23862
    Downloads
    0
    Uploads
    0
    Rep Power
    35
    If your building a mahcine that big, spend a little money and get Bishop Wisecarver dual V track and wheels. Or the knockoffs at www.cadcamcadcam.com, which are about 1/2 the price. You'll save a lot of time and aggravation, and probably money too in the long run.

    Gerry

    Mach3 2010 Screenset
    http://home.comcast.net/~cncwoodworker/2010.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  4. #4
    Registered
    Join Date
    May 2005
    Location
    USA
    Posts
    219
    Downloads
    0
    Uploads
    0
    Rep Power
    9

    Bishop Wisecarver

    Check out http://cncshare.blogspot.com/. I think he's making a x=24' axis on his megabot router. I had scrounged up some new dualvee bearings W4 size some time ago and he bought 16 from me when I put them in the classifieds. These bearings can support a lot of weight. You can see a picture of 4 bearings and a 36" rail in the classifieds/misc parts section for an example. I still have 15 bearings W4 size, 36" rail, and an 8' rail. These are too big for my current projects but if you are interested maybe we can work out a deal?



  5. #5
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10
    Quote Originally Posted by arlenw
    One of the solutions I am considering is to take cold formed square stock and place the sections end to end rotated 45 degrees with machined supports made with a "V" top and a hole through the center to allow a bolt to come up through the flange on channel or I-Beam supports and thread into holes drilled and tapped approximately 50% of the diagonal of the square stock.
    Arlenw- I think I understand what your saying and this is along to the line of what I was thinking. It's really a combination of my route A & B. The only issue I see is that you'd need to somehow hold the v-roller down onto the the cold rolled steel [CRS]. This would require another track and roller system, and I would think it would be required regardless of weather you use a rack/pinion or not. I don't think using a rack/pinion to hold the gantry onto the track is a good idea. There could be much variation in the installation of the rack [ it only comes in 6' sections] and it's been recommended many many times to use a pressure driven spur to rack connection. This means the spur gear can move and match the variations in the rack, while maintaining pressure into the rack and keeping backlash to a minimum. The Solution I'm leaning towards is actually my route A. Juswus, wus kind enough to add that link to a fellow's blog on his machine and it prompted some memory item's to come forward. I'm planning on a similar type of tressel style side rails and so I think I can make the route A work. I looked at some of the sugested sites however while the cost isn't huge in smaller quantities, when you start adding up how much of the v-track I'd need and the number of rollers I might as well take my time and buy all the linear rails [thk] that I need off Ebay.. and that still wouldn't cheap... it would work out to someplace in the range of $3500 USD. The way I'm thinking right now is simply.. I can try it.. if it doesn't work.. I'm not out that much cash, and acording to others who have done it.. it's not to hard to get decent accuracy if its done correctly. It involves many jig's and fixtures to get things right but my time is cheap.. and the route is cheap.. it just involves more time to get it right.

    Jerry



  6. #6
    Registered
    Join Date
    Dec 2005
    Location
    USA
    Posts
    19
    Downloads
    0
    Uploads
    0
    Rep Power
    0
    Hello,
    The pinion and drive needs to be mounted on a pivot with the tangent axis primarily perpendicular to the rack. It needs tension supplied by a spring or pneumatic device anyway, to minimize backlash. It does not require a great deal of pressure to keep the gantry on the bottom rack, especially as heavy as your gantry is and the likely hood of moderate accelerations in the foam cutting process(?). A relatively small amount of verticle travel is required to compensate for variations in the mounting of the rack. Do the geometry on the errors introduced by the arc movement of the pinion and drive and you will find they are very, very small. The rack sections I have purchased in the past had the mating ends ground on the ends to insure that the pinion passed smoothly over the joints and the tooth pitch was uniform at the junction. Also consider that the further the supporting v rollers are apart the less pressure required and the less effect any particles on the track have on the gantry. Another thing to think about, I used brass pinions to minimize wear and damage on the rack when they had a lot of linear movement(long distance to travel in normal operation). Brass pinions had a reasonable life, the racks never wore out. If catastrophic debri got on the rack, it was the brass pinion that died.The pinions were relatively very cheap.
    With the cable drive and the upper roller(s) mounted on a pivot with a device to keep pressure on them, you can run them on a channel flange and let the pressure device compensate for vertical variations. If you want to use angle iron tracks, I would still weld a small bridge and stud to them at short intervals so I could shim them. Keep in mind long sections of hot rolled angle can easily vary +or- 1/8 and the straightness considerably more. Variations in cold formed or rolled square stock generally run .007 or less.
    I don't know of any place one can buy regular linear guides for a system this size for even 10 times $3500. 4 inch cast v rollers with roller bearings are available from Grainger or McMaster Carr for $10 to $11 each at their online catalogs. Load ratine 800 lbs each. Higher load ratings and larger sizes cost more. Cold formed square stock $10 to $20 a foot depending on how many supports you want to make. Precision linear systems $10 to $20 an inch, and those in this price range are not likely to have the capacity for your gantry.
    What kind of maximum velocity and acceleration are you wanting with your gantry?
    Arlen



  7. #7
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10
    Quote Originally Posted by arlenw
    I don't know of any place one can buy regular linear guides for a system this size for even 10 times $3500. 4 inch cast v rollers with roller bearings are available from Grainger or McMaster Carr for $10 to $11 each at their online catalogs. Load ratine 800 lbs each. Higher load ratings and larger sizes cost more. Cold formed square stock $10 to $20 a foot depending on how many supports you want to make. Precision linear systems $10 to $20 an inch, and those in this price range are not likely to have the capacity for your gantry.
    What kind of maximum velocity and acceleration are you wanting with your gantry?
    Arlen
    Wow Arlen, thats a mouth full! Well to answer a few questions. First of all the $3500 was a very conservative guess based on what the price of some stuff on Ebay is going.. it would take me a while at 24-36" at a pop to get the nesc total lengths that I need. NOT an attractive option. As it sits right now my system is about 1200lb's in the gantry.. that may actually come down some as I'm working on a better, trussed style, design to simplify things. However, the one cross road I'm currently at is the drive reduction style. I'd sure love to go with a planetary however I've not seen many on ebay that are reasonable cost and the cheapest 'new' quote's I've got are way out of my range. So I'm faced with waiting or just going to timing belts. So with belt's I would shoot for a 5:1 reduction on two slaved 640 steppers. This should then be put thru a 1"PD spur in to a 12DP rack. This [ if my numbers are correct ] should give me 8"/S^2 acceleration. Now if I get things down where I'd like them [ around 900lb's] then I'd have a better rate of 12"/S^2. It's still not what I wanted but.. its getting there.. If I gear it down a bit more [7:1] I could probably get closer to 17"/S^2. My rapid speeds should be over 400ipm and the typical cutting speeds could be upwards of 300. So 0 to 300ipm would take 0.42 sec's. 0 to Rapid of 400 would be 0.56sec's. Now these rates are based on the holding torque of the stepper, however if a person just doubles the time that's calculated I'm pretty sure it would be in the range.

    This is a pile of weight to accelerate like this, however I've done some calculations and some of my job's would be in the order of 40ish hr's per tool change, some job's could take upwards of 100 hr's from start to finish. I need as high acceleration and sustained feed rate as I can get. The entire system will definatly be locked down to the floor! As far as deceleration rates, I have no idea what they'll be. I'm going to use Gecko's and run them at just under 60VDC so there is some room for voltage jump's due to deceleration. There's lots more to this but I'll leave things at that. I'll hopefully have some pic's to add to the post next time.

    Any opinion's or thought's thus far? [like I'm nut's! ]

    Thanks
    Jerry

    Last edited by JerryFlyGuy; 01-25-2006 at 11:48 AM.


  8. #8
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10
    Ok another question, does anyone have a decent place to go [ on the web] that easily show's how to calculate loading and what not for linear rails [thk]?? My Z axis is going to be composed of off-the-shelf rails. However I'm faced with mounting the blocks on my gantry and then cantilevering the rail's [attached to sqr hss tubing]. The rail's will travel about 36" at their lowest [ tool on the bed] My steppers should be able to [ on the x axis] put out about 800 lb's combined force when stalled, so this is the ballpark # of which I'd like to design to.I was looking at RSR15 rails and trucks. I was going to mount the truck's about 12"c-c. Am I going to overload this? I'm not worried about some deflection at that ultimate load, I don't plan to ever get that high of force in actual use.

    Opinion's, thought's, experiance and guess's welcome [oh! and web-link's if you have them!!]

    Jerry



  9. #9
    Registered
    Join Date
    Jul 2003
    Location
    NE Ohio
    Posts
    167
    Downloads
    0
    Uploads
    0
    Rep Power
    11
    hello, just interested in this thread. Can i ask why the gantry needs to be 1200 lbs? this is quite a bit of mass to sling around. Also foam would have basically zero resistance. Have you considered two machines, so that one can be optimized for foam and the other for mdf. If you optimized this machine for foam, I would use a lightweight triangulated bridge for the gantry. I bet weight could be reduced to half or less. Motors sizes and power requirements would also be reduced.

    just for reference, I looked up two automation sites that sell linear guides. Hiwin 25mm guides for the 20x10 setup, would be approx $3300 US. Using THK 25mm HSR guides for the same setup, would be approx $4300 US. These are new. The prices don't include z, since you already have them. I don't know if these are even the best prices around. If you are going to use this machine to make money, I would consider using linear guides.

    Also all of the linear guide manufacturers have specs and ratings for their products on their websites. Most also have design guides as well.



  10. #10
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10
    Jimbo, all good questions. There are two reason's the gantry is ending up so heavy. The first is.. well as a mechanical draftsman in the industrial industry, I just naturally build things heavyer than they need to be.

    OK, in all seriousness, I don't think the weight will hurt me as far as performance, other than in the accel and decel rates. The reason it's become so heavy, is because of my desire for stiffness in the gantry. The entire structure is composed of trussed members of HSS tubing I was looking for as little deflection as possible while keeping the weight down as much as possible. My first gantry design was alot more than 1200 lb's!! I'm actually working on R6 of my design and have the gantry down to ~ 800 lbs. As of my last FEA check's it will take a 500# down force [ an overweight y+z axis assm] in the middle of the gantry as well as 600# horz in the x+ and 600# horiz in the X- offset to the top and bottom of the gantry [ putting a twisting load into the gantry] and it will only deflect less than 0.007" overall. While this is lots of deflection in a machine tool environment, the only time it should ever see loads this much is when the roof falls on the gantry while it runs the z axis post into something imovable at nearly full tilt. Or I try and machine something that the system was never designed to machine.

    I've attached a screen shot of the complete unit less a few parts of the y axis. It should give you a better idea of all that it's made of.

    Btw, where did you price out those linear rails? If, as you say, those are new price's, it may just be in my best interest to buy them and use them instead of my hair-brained DIY rails. And yes, I do plan to operate this unit for profit at some point.. Ahhh.. the grand schem's of mice an' men eh?

    Jerry

    Attached Thumbnails Attached Thumbnails -r6-full-assm-isopic-resized-jpg  


  11. #11
    Registered
    Join Date
    Jul 2003
    Location
    NE Ohio
    Posts
    167
    Downloads
    0
    Uploads
    0
    Rep Power
    11
    Hello Jerry, those prices were from http://www.automation4less.com and http://www.technico.com/ respectively. I have never ordered from either of them, just stating the prices they have. If you do go this route, I would probably contact THK or HIWIN directly and ask for a local vendor. IKO is another maker as well.

    Your drawing helps clear a lot of things and it looks pretty good. Many machines of this size seem to omit the table and just use the floor. The sides are freestanding and bolted to the floor. This would eliminate some material. Another thing when doing mdf or harder materials, you could make a stand that would bring the part closer to the bridge height and reduce alot of the cantilevering of the z.

    Are you going to use 5 axis on this? just curious, is this for automotive or marine application?



  12. #12
    Moderator
    Join Date
    Sep 2005
    Location
    Canada
    Posts
    1660
    Downloads
    0
    Uploads
    0
    Rep Power
    10
    Thanks for the links! I've seen the technico site but not the other one.

    Quote Originally Posted by jimbo

    Your drawing helps clear a lot of things and it looks pretty good. Many machines of this size seem to omit the table and just use the floor.
    Ya I'd though about this, and I may end up there. It would be much easier to simply have the side rails and then mount them to the floor. If a person puts enough floor mounts on each side you could infact 'true' the rail a bit if need be. I'll probably end up w/ at least something for x-members as I'm going to be putting down some plywood for a deck. It will have many blind nuts on the back side. This will then tie down another layer of plywood which will be milled flat w/ the head and replaced as required when I screw up and mill a big hole in it [ or something dumb like that ].

    Quote Originally Posted by jimbo
    Another thing when doing mdf or harder materials, you could make a stand that would bring the part closer to the bridge height and reduce alot of the cantilevering of the z.
    I've already had some idea's for a milling table. I planned on 1/2" cold rolled pl [ 4 x 8 sheet] on legs which can be tied down to the floor/bed and then used this for milling sheet stuff. The legs would be finitely adjustable via threaded adjustment rods to get it level. It should be simple enough to do.


    Quote Originally Posted by jimbo
    Are you going to use 5 axis on this? just curious, is this for automotive or marine application?
    Well since you asked I am planning to try and do a 5 axis system. At this point however I only want to get the three axis going. I plan to do many different things with it in automotive, marine and aviation. I've got some pic's of some idea's I have for this unit [you can find them here] . I've also got some hopes of doing some investment casting in various form's and hope to do some niffty things in this area also.

    Time will tell!
    Jerry



Page 1 of 7 1234 ... LastLast

Tags for this Thread

Posting Permissions



About CNCzone.com

    We are the largest and most active discussion forum from DIY CNC Machines to the Cad/Cam software to run them. The site is 100% free to join and use, so join today!

Follow us on

Facebook Dribbble RSS Feed