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How to order the correct ball bearings and threaded rod so that they will seat well and not be loose or have play? Answered

I am trying to design, what will essentially be a very specific miter box / saw guide for a hand saw. Here is a product on the market that is almost exactly what I am trying to build. The only difference between what I need to build and this miter box, is that the miter box from that link cuts at a 90-degree angle to the workpiece being sawn, whereas I need to saw boards at angles much more acute than 90-degrees.

There are commercially available adjustable miter-boxes, such as this one, that allow you to set whatever angle you need, and it will still guide the saw straight. However, they are made for cutting baseboards and molding, so the angle-range is only 90-degrees to ~40-degrees or so. I am cutting wooden boards for making, "scarf joints". So, I need to saw through 4" thick boards at an 11-17 degree angle. Where the above miter box saws perpendicular to the board it is sawing, the one that I am building, at 11-17 degrees, will be closer to cutting parallel.

The housing, I think I can cobble together from angle aluminum and hardwood. However, I haven't bought ball bearings since I was a kid riding skateboards. I was hoping to take a threaded rod and push it through the hole in some bearings, then use some spacers and/or washers to space them apart, and secure the whole bearings/spacer/bearings sandwich with some washers and nuts. I do not live near a place that actually sells bearings much less carries bearing and threaded rod in the same store. Therefore, I cannot try it all out right there in the store. So I am going to have to order the bearings and the threaded rod off the internet.

I need bearing where...

  • Heavy load is not an issue
  • How fast they spin is also a non-issue.

But that are...

  • Shielded from the sawdust (do not have to watertight)
  • Fit snuggly on a threaded rod and not rattle around. A loose guide-bearing isn't much of a guide, eh?

Would one of you fine gentlemen help me by pointing to where I can buy 16-20 bearings, a threaded rod that will definitely fit them, and some .50 - .75" spacers (metal or nylon) that will also fit the bearings?


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1 year ago

IF this were me and I didn't have the means to turn the rod down to fit the bearing I would buy a rod to just go through the hole in the bearing. Check the specification for your bearing for the right size or measure it.

Run a nylock nut onto the rod but the wrong way round, put on the bearing and run another nylock nut on, again backwards - because of the shape of the nut this will nip the centre of the bearing neatly.

See image - click to expand.

you can make a suitable sized hole for the outer diameter of the bearing.


1 year ago

1. That is an awesome miter box, never seen one like that before.

2. I don't like miter boxes, I made a magnetic guide for my Japanese saw, and highly recommend it:
I believe towards the end of the video I show how to use it with a speed-square, hopefully that would work and be accurate enough. I use it to cut wood at 90 degrees and it's super fast and very accurate. Just in case you want to change your plans completely, or make for future projects.

3. Skateboard bearings are garbage! :) I've taken apart stepper motos and they have really good quality bearings in them, but skateboard bearings have way too much play and they make a rattling sound often.

4. Buy locknuts instead of washers, and tighten them with the rounded part of the locknuts onto the inner race of the bearing like>>> [)0(]

5. Maybe also get some plastic (POM?) pipe that you can cut to size and have it cover the bearings, to not dull the saw teeth, if hit accidentally!

Jack A Lopez
Jack A Lopez

1 year ago

I think the most common, ubiquitous, skate bearing out there is size "608", for which the diameter of the inner hole is 8.0 mm. This bearing's outside diameter is 22 mm, and it is about 7.0 mm thick.

This is just a hair bigger than a (5/16)-by-18-tpi threaded rod, and I have confirmed this just now, with a couple of samples of each, the bearings, and this size threaded rod, that I happen to have in my junk collection.

Where I live, in the Former United States, this size threaded rod can be found in the big-box hardware stores like Lowes, HomeDepot, etc.

The 608 size skate bearings themselves can be perhaps be found locally too, in discarded skateboards and skate shoes, if you have any of those handy. If you, or the local dumpsters or thrift stores, presently do not have any discarded skate shoes, then of course you can order new skate bearings from eBay, or wherever.

The fit of the 608 bearing to a size M8, (nominally 8 mm) metric threaded rod, might be better. I have not tried this, but then I think the gap between this bearing and 5/16 size threaded rod is so small, that gap could be closed with a single layer of plastic tape, e.g. PVC electrical tape, wrapped around the threaded rod.

In my searching, I noticed the RepRap forum, has a page dedicated to the ubiquitous, size 608 skate bearing, and discusses what kind of rod fits it, and other infos too, here:


Regarding the dimensional pictures attached to this post, I found those via an image search for, "skate bearing dimensions", here:


So, you know, if you want to search for dimensional drawings of arbitrary sized skate bearings, that is how you do it.

Regarding spacers, I don't know any spacers. I was born and raised on Terra, Former United States. I might have already mentioned this.