I want to be a metric purist

This is a bit of a ramble with a TLDR of "I would prefer to work solely in metric."

The eccentric spacers from the OB store (and any other store I could find them at) are a mixture of metric and US. The I.D. is set for M5 screws and the length is 1/4". I cannot find M5x8mmx0.25" concentric spacers, they don't seem to exist unless maybe you can have them custom made ($$$).

This would be partially ok if not for the cheap spacers the OB store has been using (no offence Mark). The I.D. of those spacers is much too large (7mm) and material is much too thin (0.5mm). This is causing my bearing bolts to skew just slightly when tightened. This in turn makes the bearing too tight or too loose depending on how the spacer is sitting. The eccentrics are only designed to tighten the carriage to the rail, not make up for mis-aligned bearings. If the spacers were the correct M5x8mm spacers, you'd have an I.D. of 5.0-5.2mm and an O.D. of 8mm with a material thickness of 1.4-1.5mm. Even better if we used M5x10mm spacers as then you get a solid 2.4-2.5mm material thickness and the spacer becomes much more stable. Of course, this again comes back around to the fact that the length we need is 1/4" due to the eccentrics using a mixture of sizes.

So, since we have this mixture I thought maybe I would try to find a way to normalize the eccentrics to metric lengths. 1/4" in metric is 6.35mm and my idea was to find a M5x1.35mm shim but I've been unable to source that part.

Since I cannot source a shim to normalize the eccentric spacer, the other option would be to source metric only eccentric spacers. I cannot seem to find those either, at least no in the sizes we need.

My current solution is to loosen all the bolts, assemble the pieces and slowly tighten them back working top down in an attempt to let the weight pull them all into the same alignment. I've yet to get it perfect but it's a little better. If there is a better way, please let me know.

Perhaps I'm totally misguided on the spacer issue causing the bearings to be misaligned. Please tell me if I am.

Even if I am misguided there, the mismatch of US spacers on an otherwise metric machine cause another issue, at least on the OX. The Y carriage uses a 65mm bolt with 2 wheels to span the double width Y beam. The spacing of the slots is 100% metric, but it's impossible to get the wheel spacing correct using a US spacer and metric shims. You can get close, but if you look at where the wheels ride, they are not correct. The slot centers are 20mm apart, the wheel center to outer edge is 5.5mm. That's 20 - 5.5 - 5.5 = 9. You need exactly 9mm between the bearings on each wheel. Using a 1mm shim on each side you need a 7mm spacer, not a 1/4" spacer (6.35mm). Frustrating, but solvable by finding an M5x8mmx7mm spacer at another shop.

I love working with the OB v-slot rail, but I wish that all the parts were 100% metric.

Comments and suggestions are greatly welcome.

It was bound to happen. I don't know how the Yanks manage in a Metric World. I did not grow up a "Metric Person", but have had to adapt, and to be quite honest, I find talking and working in Metric a lot easier to understand and visualise, than I used to in Fractions. I guess we went over to it, mainly because "they" are so close to us, just across the water, but the USA is a long way from the Metric Zone.
What you have written about, just about blew my mind, although I got the gist of it.
I don't know what the answer is, but it certainly needs to go, one way, or the other.

Cheers
Gray

If dual wheel configurations are going to continue to be developed, a 9mm spacer really needs to happen. I can work with the 1/4" spacers at the end as the offset to the plate is really not important but we need something to properly set the distance between the wheels fairly soon.

Actually the USA is jammed between two metric nations. Canada, which is officially metric but still uses some imperial in the private section, an Mexico.

Well, I never imagined Mexico as being Metric! Would have thought they would be wrapped up in the Dollar.

Gray

The US is one of the non-metric holdouts left in the world.

And yet, the Dollar is based upon the unit of ten. That is really odd, but interesting? It's just the "Imperial" weights and measures you're all hanging on to. That must be due to our Colonial brothers bringing it over with them, those "few" years ago. Still, they hung onto our Language as well, so it's not all bad. They did better than us.

Gray

Is there any currency out there that isn't?

As for the US going metric, it won't happen. Too many highway signs would need changed.

Well we weren't, we used 12's and 10's, till they got us. I must admit, for our kids of today, currency is real easy to understand and work out. I think our pounds, shillings and pence, was the most complicated form of currency there was! We still hang on to Miles, because as you say, it will cost a fortune to change the road signs.
I don't think the US will go metric, but I think it will be used, more and more, until it quietly slides in there between the shoulder blades.
Gray

That's great analysis - I am also building a double width axis and have noticed that the wheels do not sit correctly, using the 1/4" spacer and various shim combinations.

Can you say where you found your M5x8mmx7mm spacers?

Well, I was apparently mistaken and 7mm isn't generally available.

that being said, a 6mm and 3mm without shims will give the needed 9mm spacing.

3mm and 6mm are common.

After much googling, I find I cannot source the metric spacers that I need. However, experimentation yields a satisfactory span on the double width Y Axis using multiple 1mm precision shims. Couple of questions arise:
1) is this acceptable? I recognise that it is not very elegant, but are there any technical reasons why it may be a bad idea to use this many shims?
2) using the "Ox approach" 1/4" spacer and 2 precision shims solution - I just can't get the correct wheel spacing. Curious if anyone else is hitting this (other than @Lee Saferite who started this thread!) - I'm not sure why this hasn't been flagged up before buy all the Ox builders - unless the ~1mm play is within overall tolerance?

Although I haven't looked, isn't it possible to find some small diameter tube, with a suitable sized bore, to be cut to length? It doesn't have be a "Spacer". Anything will do really. There must be something in the plumbing game that would adapt. Someone on an earlier thread found some pipe and cut it to size.
By the way, my nickname is McGuyver. I can usually find something which will adapt.
How about micro-bore copper pipe? I think a store we have here, called B&Q, used to sell piping like that.
Model shops must do something similar.
If that is nine washers, and the black one is the wheel hub, why does it have to be round. It looks like a cube of something about 9mm in size, with a suitable sized hole drilled through it, would clear the actual wheel, sit on the hub, and meet the purpose. There seems to be loads of room there.

Just a thought. Haven't hit that problem yet myself.

Cheers
Gray

Oddly, using those 1mm shims is significantly better than the current spacers OB is selling. The shims have a 5mm ID and 10mm OD, do they provide excellent stability.

You could source 3mm and 6mm spacers and drop the shims between the wheels.

Using metric V-slot and those 0.25" (6.32mm) spacers you'll never get the wheel alignment perfect. You'll be 0.32mm too wide or 0.68mm to narrow.

You need exactly 9mm between the wheels.

EDIT: Stupid auto-correct

Woohoo, that's great news!

All the parts are coming. All the parts are coming.
All the parts are coming. All the parts are coming.
(Sung to the Coca Cola Christmas advert)

Gray

Thanks - I did try to cut a longer spacer to length, but it was a disaster. Got me thinking though with your plumbing references that I could have used a pipe cutter for a better cut. I think the pipe would be too thin for the stability, but top marks for ideas!

thanks - sounds like the spacers might appear on OB soon !