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Discussion in 'General Talk' started by Metalguru, Apr 28, 2016.
Anyone know of a source for 1/4" thick eccentric spacers with a 6mm or 6.35mm (1/4") bore?
The won't be pretty, but could you drill holes in 1/4 inch plate then cut small squares? I did this to test something and it worked.
You looking for eccentrics for steel vwheels?
No, Joe Santarsiero | OpenBuilds, the steel V-wheels use the standard 5mm bolts. AFAIK
Giarc | OpenBuilds, how would you make the larger diameter circular shoulder?
I was thinking of increasing the strength of standard v-wheels by changing out the bearings and spacers to 1/4" or 6mm bore. I am of the opinion that the M5's are one of the weak points of the V-wheel setup.
I can easily get MR616-2RS bearings, 6x16x5mm. Actually, the 1/4" bearings are R4-2RS and they are just a tad out of spec, 6.35 x 15.875 x 4.98, so they might not work. About 5 thou undersize. Thickness difference of only .7 thou should not affect anything...
Might be able to drill out the existing 5mm eccentric spacers to 6mm...
Nope, just did some calcs and I would have to increase the bushing side diameter to 8mm, and the hex diameter to just under 9mm.
D-oh. Brain fart. I didn't read your original post right.
The easiest solution would be to make your own. DIY Eccentric Spacers for less than 40c each (link originally posted by @jzhvymetal in DIY eccentric spacers even cheaper | OpenBuilds) This design was based on M5 screws so you would need to modify it a bit but would still be fairly simple to make.
@Colin Russon was looking at manufacturing eccentrics based on M8 screws for one of his designs. Don't know how far along he is with the process or if he will be selling them individually. M8 screws would provide fairly robust axles however and would work nicely with the 688Z bearings.
It's possible to both increase strength and get press-to-contact eccentricity simultaneously using 688z (8x16x5) bearings. You could even reinforce the axle contact by eccentrically-through-drilling some 8mm steel rod stubs on heavier/more vibration-prone machines. I didn't like using the eccentric spacers, so I've been setting up to do it on my next project, I'll report on how it goes.
Hey Rick 2.0 | OpenBuilds. I did see the article somewhere about the M8 eccentrics, but I thought that was a bit of overkill. Something like the guy who had 50 or 60 wheels on his OX-like build. M6 should provide a substantial increase in strength without too much modification. It probably isn't possible to get the low profile head metric bolts in M8 either. I need to have the head recessed completely flush in a 1/4" plate.
As far as making your own, I would think it would be difficult to make any quantity of these things so that they were all exactly the same size and offset. The offset would not be that important for accuracy, but the height and OD would be critical, and the faces would need to be exactly parallel.
On a small metal lathe, these things could be made out of hex stock with a 4 jaw chuck to drill the offset hole. I was also thinking of using my existing mill to make them, but I would need to machine both sides of a 3/8" plate and I don't know if I could do that accurately.
Rob Taylor | OpenBuilds I'm not quite sure what you are suggesting. Can you perhaps throw up a small sketch? Picture is worth 1000 words...
Take a closer look at how they were done in the link. All those problems were solved. He drilled out stock hex nuts and pounded stock dowels into them. The stock nuts provided a constant thickness and parallel faces and the stock dowels provided a constant diameter. Follow that with a simple jig setup in the drill press and all the offsets come out the same.
What if you cut slots in the gantry plate where you normally had larger holes for eccentrics. Then, make 1/4 inch spacers with normal diameter holes for the axles that line up with the slots. Using angle at the bottom of the gantry, tap holes and have screws that screw perpendicular to the spacers pushing on the bottom of the spacer forcing it up.
Here are a couple screen shots of a VERY crude drawing. The wheels and axles are missing, it was just done to illustrate my lamely described concept above.
Yeah, I was thinking about that. That's the way they do it on the larger machines that use 6 or more bearings that run on cold rolled steel flat rails, like CNCRouterParts.com, and finelineautomation.com.
But what's the angle piece for?
I was just trying to think up a quick way to make the screw that raises or lowers the spacer perpendicular so it could push on the bottom of the spacer do make it go up or down. It doesn't need to be a threaded angle. There are other ways to do it. That was just three different views of the same thing.
I gave that some thought. It might work, but there is one flaw: The axle bolt is in a slot that is parallel to the major force on the wheel. This means that there may be a significant twisting force on the wheel/axle, and there is nothing to support it in that direction because of the slot. Also, the setscrew acts as a fulcrum. The only support it gets is from the bolt head and the spacer which are flat surfaces resting on the perpendicular faces of the plate. Might be ok, especially if these flat surfaces are larger.
I thought of something like a bicycle chain adjuster, where you have a u-shaped bracket with a screw into the edge of the plate. The u-bracket has a hole on each side for the axle bolt to pass through. Plate still has a slot, but the u adjuster keeps the axle bolt aligned. Might be difficult to drill and tap the hole in the edge of the plate... You could extend this so the u channel runs the full width of the gantry plate and all the wheels attach to it. This would also allow you to use any size axle bolt -6mm, 8mm, etc.
I just had a look on Mcmaster Carr, they have a 1/2" wide aluminum channel with 1/8" thick walls, and the depth of the channel is 1" outside. That makes the channel 1/4" x 7/8" inside, perfect for this application... Part number 4592T12
That is a great find, and great idea. Much better final product than my idea.
Why thank you.
It's nice to have intelligent people to bounce ideas off of as well. This is one of the big pluses to the Open concept. Keeps the creative juices flowing, as it were.
I still have to do a full size model of this and see how it works in the real world.
McMaster Rules. They Have Everything
I like McMaster. The only thing I dislike is that I don't know what the shipping costs will be until I submit my order. I always get a bit nervous especially when I ordered the 6 foot acme rods. It was very reasonable, though.