Looking for advise on best way to have some T slot extrusions machined for mounting of linear rails. I realize most people dont but if you look up specs for linear rail mounting the aluminum extrusion has to much variance. I am building a large format 3d printer so small differences are going to be exaggerated. I can buy them Pre machined from Misumi but it is about X5 as much as standard. Appreciate any advice
Iâve got a bunch of t-slot track I use for my woodworking tools and itâs always dead straight. Are you saying itâs not? You could always cut your own into the wood without using a track too. A router with a straight edge and a slotting bit would do the trick.
Or maybe Iâm way off base and this is not what youâre referring to at all.
for general purposes you are correct they are straight but straight is a relative term when it comes to machined tolerances. Since a Linear guide is a very precise linear motion system it comes with recommended tolerances for flatness. For many applications this is well with in the acceptable limits. I have even heard Ryan comment on Aluminum extrusions not being straight, I believe he said they come out of the machine like a hot noodle, haha.
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Well, yeah. They are technically hot noodles as they come out of the extruder. Extrusion seems like an inherently imprecise manufacturing method. Machining the track from a solid bar of aluminium would be much more precise. Also much costlier and time-consuming.
I assume the title âmachining T slot extrusionsâ refers to taking an extrusion, and then machining it to more precise tolerances? Which is sort of like using the extruder as your roughing pass, and then going back in for a finishing pass.
correct and good description. basically only need to surface the side the linear rail attaches. I could be splitting hairs here just trying to really think out all possible issues since my build volume is so large. 900mm in x and 600mm in y
To get the top surface flat, if you already have machinist quality tools, then there is hand filing and way scraping. Both can achieve VERY flat, straight and square surfaces.
If youâre careful, maybe a surfacing bit in a lowrider can get you there.
If you need to machine the bottom of the t-slot, then youâll definitely need a well tuned lowrider and some skill.
Chasing accuracy gets very expensive and time consuming, very quickly. 
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What is it, every â0â to the right of the decimal of accuracy costs at least one â0â to the left of the decimal in cost?
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I havenât heard that before, but it sounds like a pretty good rule of thumb!
I agree with both of you whole heartedly. I am way more of a 3d printer then I am a machinist. The exact reason I asked all the Machinist I know, haha. I think I might be focusing on a trivial part of the build process but I am trying to knit pick everything before I start cutting and assembling. I could easily just convert a MPCNC for the task but I am trying to build a large printer with the same print quality as a small one. Post processing is huge part of cost on any product so the better is comes of the machine, less work and money to have a finished product. Appreciate the advice but I feel leadscrew accuracy and backlash is far more important then me knit picking the linear rails.
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