Mendel bearings

48 bearings is a lot... especially at those prices.
I'm assuming I can change them out for other bearings to try and save on cost.
i.e. 1/2inch OD bearings (12.7mm) 3/16" ID (4.76mm). I can just screw them down tight to take up that 0.76mm slack, or just drill out the hole bigger and use 3/16" nuts.
What do you guys think?

I thought the same thing. I plan to use R3 bearings (0.1875 ID) which are very similar to the 624's (4mm = .157" ID) but are way cheaper and easier to get a hold of in the US (which I assumed you were in based on dimensions you used).

I found a lot of 50 R3's on eBay for about $35, free shipping. This was the best I could find after much looking.

I was hoping the R3's would trade out directly, but I think the .030" difference in ID is a little too big, so I was going to use the corresponding US hardware in place of the M4 bolts in these areas. Might mean widening up the holes in the RP parts with a hand drill to get the bolts to fit.

Nik

EDIT: by the way, 3/16 bolts don't really exist. The closest ones are #10-24, but those can have an OD up to about .190 so there might be an interference...I gotta remember this when it's time to buy my Mendel hardware (repstrapping now)

Edited 1 time(s). Last edit at 11/28/2009 01:49AM by toomanyplugs.

the bearings were about AU$1.20 each here.. maybe they're cheaper in countries that have actually managed to convert to metric?

I am based in the US. The R3 series was the one I was looking at. I'd rather pay +-63 cents each (same price you got $35 for 50) than the $1.40 USD I normally see as the cheapest 645. The nice thing about trying to get it cheaper... if I use the R3 I can use standard nuts and bolts in imperial at my local hardware store if need be.
I would prefer to work in metric though... no fractions, easily move the decimal to work with different units, mm, cm, m etc. It's what I used to use before coming to the US.

I'm working on repstrapping a mendel out of wood until I can get the RP parts made. so far I have a good design on the frame... the axes though... hmmm
good luck and if mine works I'll post on here or the builder blog

100 608ZZ for $34.95 plus shipping
[www.vxb.com] (US based)

M8x1.25 cap screws 25mm long, 50@$8.85 plus shipping
[www.mcmaster.com] (US based)

The specs say 624 bearings for most of the machine, so these aren't exact fit, but it sounds like you are deviating from the plans anyway.

At these prices, unless you need it now, I think you are crazy to go to the hardware store for supplies. Doubly so since you talk of drilling out the bores yourself.

I can't think of a quick and easy way to fixture the bearings so the inner bore does not turn. If you could solve that problem, it would probably take 2 hours to drill out 48 bearings. How much is your time worth?

To follow up on a positive note, here are a few ideas I'm tossing around to cut the cost on my Mendel

1. construct the frame out of angle iron which I keep finding near dumpsters (as bed frame) and carting home. (Mend-angle anyone?)
2. use part of a used shock absorber for the Z-axis rod. It's stainless steel, ground smooth, and dimensionally stable. The only issue is that it's thick and short.
3. Direct-drive a lead screw for Y and X too. This will give me a finer resolution at the expense (I assume) of slower bed speeds
4. possibly using angle iron instead of rods for X and Y. This may work out with careful alignment on my much more stiff angle iron frame.
5. Screw the sub-assemblies together with self-tapping course-thread deck screws. To to this you clamp say two pieces of cutting board together, drill a pilot hole, and the switch to a larger drill bit and drill through the top piece only. Thus the self-tapping screws only form threads on the lower piece.

That's a great price for 608's, which are what the McWire cartesian bot uses, but not Mendel.

608's are 8mm ID 22mm OD, whereas the 624's are 4mm ID and 12mm OD. That's a big difference that means you can't really use the 608's in Mendel without significant redesign.

For comparison, vxb has the 624's 100 for $99 [www.vxb.com] or 10 for $20 [www.vxb.com]
and the R3's 50 for $50 [www.vxb.com]

(yes, the 624's are only $1US a piece, but I'd rather not buy $100 of a lot of anything when I only need half as many. I'm trying to minimize overall project cost, not amortizing over many projects. $35 for 50 R3's vs $100 for 100 624's is a reduction in cost of 65%!)

The obvious solution is to get together with another Reprapper and split costs. I'm in for 50 624's. I'll pay half of your shipping costs, plus the full cost of shipping it (using regular postal mail) to me. Please send me PM if interested.

-Geert

I agree with Plugs, I want the right amount at less price, not more just to save on per unit... unless I want to build more or make kits to sell.
For some of the stuff on the BOM list it's like 104 when mcmaster sells them in sets of 100... I'll go to the hardware store and buy the extra 4, unless I just have them sitting in my bin.
I already bought my R3 bearings on ebay adn 64c each, better already than $1ea for 100. You're right, my time isn't free, but I live on my own, pay all my own bills and have limited income, so I am willing to put the time into whatever it'll take, it's not like it'll take less than a few hours to even find the right parts, let alone put the machine together if you had ALL the BOM materials as listed.
Since I don't want to spend an inordinate amount of money on RP parts, I've started making the framework corners out of wood, and it's working well, my drill press even makes the holes at the right angle (no pun intented since it's30 degrees each side.)
I do think that people should get together to split the extra stuff like Geert said. I thought that's what the rrrf was for, but it looks like they went bye bye since it's redirecting me to reprap.org.

I'm hoping to have the main frame done and shown on the builder blog in the next day or 2.
good luck to all.

If you're doing the R3's you should be fine with 10-32 bolts. I've used them with 3/16 hole aluminum grommets and they slide through fine (the grommets are made for AN-3 bolts, 10-32 is much cheaper for things that don't need AN-rated hardware). Also, the Mendel bearing mounts have a bit of flex to tighten them onto the rods so you should be able to take up the extra .5mm of slack.

As far as splitting parts goes, you should include your surplus parts with the Mendel RP sets you print off and charge the benefactor the difference. That way, you both save from buying in bulk.

Although, I got burned by this idea when I bought 5 mm bolts for Darwin and Mendel doesn't use them.