Ball Bearing Sled Runners

[al ladd]

In my continued obsessive research and development into the world's best table saw cross cut sled I’ve developed a method of using inexpensive ball bearings as a table saw cross cut sled runner that’s second to none, and easily installed by anyone with a drill press and the ability to make a precisely dimensioned spacer stick. The system can be used to make sleds of any length.


Ball bearings between ½” OD and .748” OD (12-19mm OD) are suitable. Best ID’s are between 3/16” and 5/16”, and thicknesses 9/32”-5/16”. Suitable bearings can be found for sale in ten packs on Ebay for under $10 delivered. 19mm OD bearings will require a very thin spacer for most saws, and you might find a piece of sandpaper or other paper stock the right thickness. You can always augment the spacer thickness with a length or two of cellophane or masking tape. You will need 8-10 bearings depending on sled length, and each bearing requires a shaft 5/8”-3/4” long. Either dowel pins or roll pins (spring pins) the correct diameter to fit the bearings ID make good shafts. These are available from industrial suppliers like Mcmaster-Carr or Zoro.com, or from Ebay vendors.


The spacer must be the exact thickness to create an offset between pairs of bearings to fill the miter slot width. So ½” OD bearings will require a spacer stick .255” thick for a miter groove that’s .755” wide. It’s easy to try your spacer with 2 bearings before committing holes to your sled, and then further testing out your offset bearings with a mock up made with a piece of scrap wood a couple inches wide and about a foot long. If there’s any play, you can add strips of cellophane tape until you get a zero-play fit. You can tell you’ve gone too far with spacer thickness when you get a little binding and a tendency to lift while sliding. The beauty of the system is the ease with which you can dial in precision to within a thousandth of an inch or so, and then installing the runner is as easy as banging 8-10 shafts into friction fit holes. The ball bearings exteriors are hardened steel, and they roll, so they are unlikely to ever wear out, as contrasted to the nylon discs or set screws of some commercial miter bar systems that can wear within a few dozen passes up and down the saw.


You’ll need a straight sled edge to hold tightly against a carefully set and well-clamped fence on your drill press. Use 4 bearings on the front length of sled your saw’s table allows before contacting the blade, typically around 12” for a full cabinet saw, and about 8” for a job site saw. Reproduce this pattern for the rear end of the saw, and depending on sled length you’ll usually need another pair of bearings or none at all between these two sets. Mark the locations, and then mark every other hole location as to whether it will be drilled with sled edge right against the drill press fence, or with the spacer between. Drill holes with a brad point bit. Drill deep enough for shaft, and if that’s not all the way through, finish the hole through with a slightly undersized bit holes so shafts can be driven out for troubleshooting or eventual replacement.


Spring pin shafts are easy to get a friction fit in the sled, as they compress when driven into a proper sized hole. Try to support the inner race when you drive spring pins into bearings to prevent bearing damage—though the bearings should function well enough for our purposes even if they get slightly loosened from pin installation. Dowel pins are easier to drive into the bearing than spring pins are. A 4.75 mm hole is perfect undersized diameter for a 3/16” dowel pin. You might find a similar 1 or 2 thousandths of an inch undersized bit for your dowel pins to friction fit. If you use dowel pins with holes exactly sized to pin diameter you’ll need to epoxy or CA glue the shafts into the holes.
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[Jim Morgan]

Sorry, this was difficult to follow. A diagram or two and/or some more informative photos would be helpful.

[Bill Dufour]

Just use eccentric bolts to mount the bearings.
Bill D

[al ladd]

As I went past the edit time limit, I'm rewriting my post as a reply, and adding some photos:

In my continued research and development into table saw cross cut sleds I’ve developed a method for using inexpensive ball bearings as a runner that works well and is easily installed by anyone with a drill press and the ability to make a precisely dimensioned spacer stick. The system can be used to make sleds of any length.


Ball bearings between ½” OD and .748” OD (12-19mm OD) are suitable. Suitable bearings can be found for sale in ten packs on Ebay for under $10 delivered. You will need 8-10 bearings depending on sled length, and each bearing requires a shaft 5/8”-3/4” long. Either dowel pins or roll pins (spring pins) the correct diameter to fit the bearings ID make good shafts.


The spacer must be the exact thickness to create an offset between pairs of bearings to fill the miter slot width. So ½” OD bearings will require a spacer stick .255” thick for a miter groove that’s .755” wide. Before committing holes to your sled test out your offset bearings with a mock up made with a piece of scrap wood a couple inches wide and about a foot long. If there’s any play, you can add strips of cellophane tape to your spacer's thickness until you get a zero-play fit. The beauty of the system is the ease with which you can dial in precision to within a thousandth of an inch or so, and then installing the runner is as easy as banging 8-10 shafts into friction fit holes. The ball bearings exteriors are hardened steel, and they roll, so they are unlikely to ever wear out, in contrast to the nylon discs or set screws of some commercial miter bar systems that can wear within a few dozen passes up and down the saw.

You’ll need a straight sled edge to hold tightly against a carefully set and well-clamped fence on your drill press. Drill deep enough for shaft and finish the hole through with a slightly undersized bit so shafts can be driven out for troubleshooting or eventual replacement.

James, thanks for the suggestion for more images and fewer words. I hope these edits might help.....

Bill, I don't think eccentric bolts that would work for this application are available off the shelf, and custom bolts would be prohibitively expensive. I wrestled with the idea of making aluminum eccentric mounts that might work, but I don't think I could have done that affordably. This system costs less than $15/runner at retail cost. Buying bearings and shafts in medium sized lots brings the cost per runner down below $4.

I was very pleasantly surprised when I tried the method I outlined, and found it was easy to get a perfect fit, and have since replicated it several times. This method is easier than using eccentric mounts even if the perfect mount could be had affordably. It only takes a few minutes to size the spacer.
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[Cameron Wood]

How long have you had this in use? Is it 1/2" MDF that the pins fasten in to?

[al ladd]

How long have you had this in use? Is it 1/2" MDF that the pins fasten in to?


Cameron, --I should warn that this idea isn't time tested --just prototype with limited use. It feels robust. Mostly I've worked with strips of sheet goods rather than actual sleds. The sled shown in the photos above is made from 1/2" Acre, a plastic and rice hull sheet good that has some nifty properties for a cross cut sled. It's rather soft, but the bearings seem robust within it. I think Baltic birch would be the preferred material for this system, and it's the commonly preferred material for a good sled anyway (though the price has gotten higher than historical, it's still affordable as a sled material). But I think MDF would be fine. As long as the material will accept a clean hole. A more robust system could be made by using aluminum spacers for the shafts with a nut and bolt augmenting friction. In fact, I think I'll pursue that!

[David Stone (CT)]

Very clever. Question: Do your prototypes suggest that this approach would be especially advantageous on a sled with just a single runner? It seems to me this might be so, given that two runner systems may perhaps better tolerate and cancel out slop associated with traditional runner materials.
Regardless, filing this concept away for some future day when it will be the solution to a need I don't yet have but will. Thanks for sharing.

[al ladd]

Dave--this technique is absolutely for use only on a single runner sled. See many posts on this forum by Dan Cameron on the advantages of a single runner sled. I agree with him, and I think the justification you and many others suggest for a double runner sled is a bit like a restaurant with inedible food, "but at least the servings are large".

That said, there is a possible variation of this technique where you'd build a double runner sled in two halves, each with a single linear run of bearings. You'd run each half through the blade with pressure on inside of groove. Then you'd join the halves with back and front fences while the two halves are held together with light clamping pressure, or maybe just tape. I haven't tried this yet but it should work great, and be really fast and inexpensive to construct.

I arrived at the idea of this system after realizing that much of the difficulty of getting a perfect sled run is the problem of fastening wood or plastic runners exactly in place, even if the runners themselves are perfect; it's hard to maintain linearity, so their effective width grows. The best remedy to that problem is fastening with double stick tape in place before securing with screws. But even then there is the possibility of losing a straight line from the distorting vectors of drilling and screwing. Thus the many reports of needing to tune runners after installation with rabbet planes and scrapers, ending up with either wobble or non-linear travel .