Can anyone tell me the official or preferred design center distance for standard rollers on 20mm V-slot extrusion? I'm wanting to design my own plates, and the only dimension I've been able to find (on a print) is 40.29mm between the 5.0mm and 7.0mm holes. Is this correct? It would be nice to have a compiled list of these center distances for standard, mini, and combined (standard & mini used together). Many thanks for anyone who can verify or correct my 40.29 dimension! While we're at it, are the 5.0 & 7.0 hole sizes correct as well, for fixed mounted & eccentric mounted rollers? EDIT: also, does this center distance target the mean position of the eccentric? - Bill
Take a look at this forum post for some more discussion: wheel offset I don't think there is an 'official' recommendation. But I'd love to see one as well. I've currently got $100 bet on @Rick 2.0 and his +20mm idea. I'll be able to see the plates I'm having cut out later this week I hope. -D
Thank you for that link, Jonathon, very helpful! I always tend to design tight, but that's gotten me into trouble more than a time or 3 I like the 20mm target just for the sheer simplicity, but I don't want to short-change my adjustability, ending up with the eccentric too close to top-dead-center, if you will, by using too wide of a distance.
As for the larger holes, they are 7.14mm (9/32") and this dimension is critical for proper fit up with the eccentric spacers. For the smaller holes 5.0mm is fine if the plate is at the nut end of the bolt but as there is a slight flare just below the head of the bolt a true 5.0mm hole can prevent the head from seating properly. I use a wire gauge bit that's 5.05mm (can't remember the number) or a 13/64" (5.15mm) and really note no appreciable difference between the two. I tend to wait to do final tightening on the bolts in the smaller holes until everything is fully assembled and they all have uniform pressure against them so they all get pushed equally to the outside edge of the hole to where the minor excess in size doesn't seem to matter.
Thank you for that clarification, Rick. While I have your attention, can you (or anyone) tell me the shoulder length of the 7.0 dia. on the eccentric spacers? Since my plates will be laser cut from steel and not c'bored, this dimension is critical in deciding the gage thickness to cut the plates from.
badlizard, you might have luck downloading the STEP parts library: STEP Parts Library Import the appropriate file into OnShape (free for public stuff) and you can then get any dimension you need from any of the parts. This has been a great help to me when designing my own carriage plates. -D
Now THAT should answer a question or two! Thanks Jonathon! Edit: found the shoulder dim I was looking for: 2.50mm
I came across an issue this weekend that may or may not affect you. I set up a standard gantry plate to fit a recently purchased piece of 20x80 and at the widest wheel setting it was having to flex the plate to fit. C/C spacing for this batch of extrusion came in at 100.91mm or +20.91 based on the extrusion width. I hadn't come across any pieces of extrusion missing this badly before this so it was a bit of a surprise. To be safe I suggest either getting the extrusion prior to cutting the parts and doing some measurements for yourself or at least setting the C/C distance based on +20.3mm as this will cover V-slot requiring everything between +19.6mm and +21.0mm. Note: measurement is based on gripping a single wheel and zeroing the digital scale in order to create an overall measurement that subtracts 1/2 of a wheel each side to give C/C distance in the display. Actual measurement would be 23.89mm larger.
I was just going to say that I just did some fitting myself using the +20mm specification. This was a custom plate on a newly-bought C-Beam from the OBPS. I was able to get good pre-loading on every wheel. But most of the wheels ended up being close to or at their tightest eccentric setting. At 20.3, I don't think I would have been able to get them tight enough. So hopefully yours was an outlier, Rick. If not then what we really need are eccentric spacers that describe a wider circle to account for the tolerances of the beams. -D
