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Open V wheel on v rail or MGM track

Discussion in 'CNC Mills/Routers' started by JFAirplane, May 7, 2016.

  1. JFAirplane

    JFAirplane Well-Known
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    Hi

    I was about to build an OX bason on C-beam and I would like to know if a linear motion is better than using the V wheel running on the small v-rail ?

    For the track, I'm looking at Hiwin MGM12. I know the big HG15 or HG20 is vey the best, but is the small MGM is mostly equal to the Delrin v-wheel... Or even the small size of those track will made a better match and outperform the v-wheel.. ?

    Thanks for input.
     
  2. Rob Taylor

    Rob Taylor Veteran
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    Linear bearings will always far outperform V-wheel, unless maybe it's steel V-wheels on steel track (which doesn't exist...?). I know the 20mm linear profile rail can deal with up to about a ton and a half of force, I'd expect the 12mm to do probably half a ton. The specs should be on there. Delrin will deform and polycarb will explode long before that linear rail starts working hard.
     
  3. JFAirplane

    JFAirplane Well-Known
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    Hi
    Indeed a steel rail could be quite the best too. I do see v steel rail, over ebay, but again, is the alu v-rail will deform a lot over time ?
    I plan on the same setup as one of the member with the Area51 cnc. Quite good working.. And again, If I put more v wheel over the rail, I should expect to spread the load much further.
    The OX is still far better than the first build kit setup made by Lumenlab, but all time, we can upgrade and there's no limit too.

    But on the linear rail, if I need a removable gantry top section, as the Area51 project, is the bearing just fall apart ? If I end up with 2 or 3 bearing less, I don't know if the system will still be efficient.. rather just plain v-wheel.

    Thanks again
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    It exist. Steel Vgroove track I haven't seen yet. These bearings are rated about 5.9 tons each. I'm predicting around 4 tons is more reasonable. Regardless, the screw grade used here would shear or something else in the system would give first.
    They have slightly higher rolling resistance, but angular contact is the way to go imo.
     
  5. Rob Taylor

    Rob Taylor Veteran
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    Not really sure what you're saying here. What exists, if you haven't seen steel V-track (which is what I was referring to in the singular)? Angular contact vs what? Angular contact ON what?

    If you mean Alu extrusion, all I keep hearing about it is that steel wheels will wear it down prematurely, hence why I discounted it without consideration. Are you saying it works? Or is your track some other steel profile?
     
  6. Joe Santarsiero

    Joe Santarsiero OB addict
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    Steel V-wheels on steel track exist. No offense, I read it as you were unsure if that existed. I was adding that I haven't seen steel V-groove track just in case you meant that. Which it now sounds like you did.

    Yeah, steel will tear up the aluminum. Al on Al is no good either. It will gall up.

    The wheels and track pictured are both hardened and ground steel.
    Angular contact refers to the bearing type.
     
  7. JFAirplane

    JFAirplane Well-Known
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    Hi

    yes the steel track can be found over ebay and the main maker is Bishop wise : Dualvee® - Linear Vee Groove Guide Wheels
    You can also find rail made by PBC Linear, but as always way too much costly.
    the Unirail from Igus could had been very great, but having the whole glide pad being tight by only a ultra tiny set screw doesn't make it very good.

    For the eccentric, do we need to adjust every time we will use the ox ? And on the X carriage, I was thinking if it's better to use a small bolt with 1 wheel, instead of a long one connecting the 2 wheel. Just like the Frog project build:
     
  8. Rob Taylor

    Rob Taylor Veteran
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    Oh, you're differentiating V-edge and V-groove track? That makes sense. I hadn't seen either, but I'm glad that at least the V-edge track exists. I wasn't really understanding what I was seeing in that photo until I saw the separate Bishop-Wise product shots.

    Angular contact bearings... Interesting. Not sure how I'd managed not to come across those before. They look like a cross between deep-groove bearings and needle bearing thrust washers. I assume you have to use them in pairs, as you would with thrust bearings (I mean, you do with V-wheels anyway, but you know what I mean)? In fact, wouldn't a pair of those replace a typical four-bearing thrust/radial/radial/thrust bearing setup on an output shaft?
     
  9. Joe Santarsiero

    Joe Santarsiero OB addict
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    One dual row angular contact bearing can replace the combination you mention. May not necessarily be the better choice. Depends on application.
    The steel wheels above have the two opposing bearings built in.
     
  10. Barry Danks

    Barry Danks Veteran
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    Steel V-track does exist. My last CnC I built with steel V Track from PCB Liear $$$ though V-Guide Rail for Linear Roller Bearings - Cam Roller Technology
     
  11. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yes Barry. That was clarified by my picture. :) I'm using it on my machine. They were a little pricey. I was talking about if steel v groove track exist instead of this upside down v profile. Kinda like Openbuilds v groove track. I imagine that would be even worse in cost. Can't really see an application for it though.
     
  12. Rob Taylor

    Rob Taylor Veteran
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    Seems like it would essentially be just over double in cost off-the-shelf, since right now you'd have to use two separate V-rail tracks screwed together and turn & grind your own steel solid V-wheels. If you have a lathe (I do), a horizontal mill (I don't) and a surface grinder (I definitely don't) it wouldn't be too much trouble to make those. It's a case of the old "need a machine tool to build a machine tool".

    On the other hand, because they're simple profiles that don't need any specialised equipment- a regular bevel cutter will do the groove and a standard surface grinding wheel will get far enough into the 90 degree slot to do what it needs- it might be surprisingly cheap to get them made at an actual machine shop?
     
  13. Joe Santarsiero

    Joe Santarsiero OB addict
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    Edit: Crap Rob. I didn't expect this to turn into an article. I'll be editing this for days!! lol. My apologies.

    I'm skeptical about making that track through a machine shop. The A track (let's just call it that :) ) are made in large quantity which offsets the cost of setup, fixturing, heat treat, any metrology, and the labor involved in those things. Youd face the same thing doing a V groove and would be better off trying to go into business to sell them...which circles back to the question of why choose them over the current track.

    Lowest cost might be to go with cold rolled angle iron or just mount bar using the stock edge between the wheel. From there maybe stock bought from cncrouterparts. It seems like a nice step up in quality from the former.
    Case Hardened Cold Rolled Steel Rail - .75"x.5" | CNCRouterParts
    The mounts for those can add up though. Btw, check out their fancy v wheel carts. They're pretty slick.

    As far as the wheels; If you wanted to be a purest in the make sense then you could certainly whittle your own with a lathe and press some bearing in. Counter to this, the ground dual Vs have gone down significantly in cost in the past 6 mos. You can find them for around or under $3 each and you can get away with fewer of them over the typical radial bearing setup (with nonsteel wheel shells). I'm using 10 per X and Y or under $30 each axis. One could build a Z with only 4 to 6 extra for under $20 more. They're nice not just only because they're rigid as mentioned, but because there is no assembly.

    Again, after eccentrics, concentrics, track, and track installation (So many holes to f-ing drill and tap you'll look like Popeye when you're done) it's not a low cost simple route. Ultimately, they will supply a very rugged, compact, and decently precise solution to linear motion, but you have to question whether or not this is within your original scope. In this hobby (and speaking generally) it's easy to go off on a tangent with the buy button! Who doesn't like Christmas five times a year?? If you can afford it then buy away, but if one just wants a beater to get their feet wet in CNC and maybe have some bragging rights amongst friends then I'm not sure this system is the most practical.

    In the end, it's safe to say that we see a lot of creativity from the diy community. Right now is the boom time for home CNC. If we distill it all down; the choosing, implementing, and improvising of all of the components involved(and accessible) to create an optimized machine seems to be the endgame. We see many implement a majority of the staple components in their system with great success. We also watch and learn from others who lose track of their initial scope and just choose randomly from these components and slap it all together with fingers crossed. I'm not trying to sell any one on this system in that fashion. It's just another tool in the shed to me. Then every once and a while we have gems of improvised creativity that add value to the community (like the F117, frog, OX, etc..to name a few here) and most of us take note, recall, and bring up these tricks to others. With that, everyone has a better chance to achieve their projects scope by utilizing the available community to evaluate their design and Openbuilds has been a great place to do this.

    *takes breath. :D

    Joe
     
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