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Is there a standard or common size or sizes (width/depth/profile) for tracks in machine beds and jigs for fences, mitre gauges, feather boards etc? If there are a few common sizes, do they vary from Europe to the US? (I'm in the UK).

I'm going to make a little router table, and was considering buying some lengths of Aluminium extrusion to fit as a track for mitre gauges and/or fences, and also buying a mitre gauge to use in it. However I'm not confident when ordering the track that it will fit any accessories.

Looking online, lots of mitre gauges are described as "fitting standard mitre tracks" but then don't specify how wide that track is. Tracks are easy to find on sites like ebay and Amazon, but come in several different sizes. In the UK "19mm track" is often advertised, which then is actually 19.3mm internal width which is (I think) a little over 3/4"

"Axminster Craft" mitre gauges say they fit a 13mm slot. And you regularly read about gauges from one machine or manufacturer not fitting the slot on another machine.

If there isn't a standard size, how can I be sure that accessories will fit the track I fit when most online shops don't specify the size?

  • Hi-rep folks, I'd love some extra tags on this question (But I can't create them). mitre-fence perhaps, t-slot or t-track or just track. I'll leave it to your discretion. – Andrew M Jun 3 at 20:24
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    To be clear: you are talking about U-slots and tracks, not T-slots and bolts? I ask because the fences and jigs you mention in the text of the question seems typical for U-slots, but you mention t-slots in your comment. U-slots are more common for typical "table" tools I know about, with T-slots being part of fancier or custom fences. – jdv Jun 4 at 14:54
  • Sorry, I was using T and U almost interchangeably. As I'm planning to buy track to fit into a wood table top, all the extrusions I've seen advertised seem to be T-slot technically but described as if they were U-slot between the narrowest part of the opening (eg, the 19.3 is the opening, the bottom of the track is wider). – Andrew M Jun 7 at 21:22
  • T-slots are shaped like the letter T (whether upside-down or now). U-slots are usually a little wider at the bottom so locking slides will tend to pull to the bottom of the track and not pull out. But we are talking a few thousands of an inch difference between the distance across the top of the slot and near the bottom. U-slots also tend to have generous corner radius so bars bottom out and don't catch on the corners. T-slots come in a few "standard" sizes, and can be cut in wood in a single pass: engineeringtoolbox.com/t-slut-t-nut-size-metric-d_2072.html – jdv Jun 10 at 15:36
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I've just experienced this very situation recently. Here's what I learned about U-style slots. I did not fully research T-slots, which is a whole other world of non-standard standards.

Imperial sized U-slots come roughly in two flavours: 3/4" and 5/8". The huge majority of after-market equipment out there, at least in the Americas, is one of those two sizes.

Of these two, 3/4" seems to be the most common nowadays by a huge margin, with older equipment (in my experience) being the smaller dimension. This makes it hard to match after-market equipment to my table saw (5/8"), but not my newer router table (3/4"), for example. So, if you pick up older equipment at auctions and yard sales, it'll probably expect 5/8ths tracks.

As far as I know, there is no standard, other than the ad hoc standard of these two sizes, with 3/4" by far more common.

A note on dimensions: U-slots are generally formed such they are not square. i.e., the cross-section dimension at the top will be smaller (by only a few thousandths) than the same dimension at near the bottom. This is to facilitate clamping/locking mechanisms so that lateral force tends to pull tracks down into the channel; that is, locking bars will wedge themselves in a bit. This is similar to how clamps and dogs can have surfaces offset a few degrees to keep work from squeezing out, or losing square as force is applied. U-slots also tend to have generous corner radiuses in the bottom to allow for free movement in the slot, and to allow room for locking mechanisms.

19mm is roughly 3/4 inch, and these slots are meant to be a bit sloppy, so perhaps the Euro sizes correspond to those, as well. 13mm is a little sloppy for 5/8ths, but it might be close enough. I mean, it depends if they are talking about the slot or the track, and if the track is meant to slide or hold during use.

As for how you know what ones you need? Well, in my case I need both. You may only need one of those sizes. Take some calipers or approximate with a ruler or scale and see what you have on your equipment. Like I said, these sizes are meant to be nominal, so there can be a lot of slop. And, I cannot stress this enough: it depends on whether the track is for locking or for sliding.

A note on U-track purpose: U-tracks have two purposes: you either want something to slide with a slight interference fit to act as a guide (e.g., a cross-cut sled, or mitre bar) or you want it to clamp and not move (e.g., finger-boards or other safety equipment). Sliding bars want a loose interference fit so things stay square. Locking bars can be a little looser because they have a locking mechanism (with a j-slot, or a cammed t-nut, or some other mechanism) that is intended to keep the bar from moving.

Milescraft after-market stuff that fits mitre slots often ship with both sized tracks. I was unable to source 5/8ths tracks anywhere but as a part of a kit from this company. They sell spare parts for their jigs and fences, so I am considering picking up more 5/8ths track from them.

You might just consider making wood tracks for some of your jigs and fences. I'm considering this for my own saw instead of buying them from that single source. This way I can keep the locking tracks on my fingerboards, and have a dedicated cross-cut sled that slides on hardwood tracks. Of course, this is yet another project one has to fit into the shop time they have...

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  • Excellent Answer, I wish I could +2. You cover and additional important, but not-always-talked-about, thing re. the measurement being the slot itself, or the track extrusion? Wood tracks are also a good inclusion since they allow most easily for a custom fit, from a tight just-sliding fit to a looser fit which might be useful for specific tools (or specific operations perhaps?). – Graphus Jun 4 at 14:44
  • Thanks. I realize too late that the OP might be asking about T-slots (or they mention them in a comment) but their question seems to be about U-slots and tracks. So, this might not actually answer the question they intended. Oh well. Maybe I'll ask for clarification. – jdv Jun 4 at 14:51
  • Could you elaborate on the requirement for a little play/slop in the track? Is that because the accessories clamp laterally (with a cam or something), and so come to rest firmly against one side of the track? – Andrew M Jun 7 at 21:53
  • @AndrewM I added a part to distinguish between the two typical uses of a u-channel. – jdv Jun 8 at 2:56
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I would suggest purchasing the miter gauges you're interested in using. Getting manufactured miter gauges does seem to be the way to go, as they seem (to me, at least) to be the more difficult part to accurately make at home (especially if you want one with angles premarked).

Once you have the gauges in hand, you can then measure the actual bar widths. You can then:

  1. Return any that are "odd-ball" sizes (i.e. don't match the majority and don't warrant a "special case")
  2. Purchase U-channel to fit whatever you've kept.
    • My impression of the UK (I'm in the US, so that's 99.99% from what I've seen on TV, forgive me) is that there are plenty of small manufacturers so you should be able to find someone, somewhere who will have U-channel in the exact size you need for the fit you're looking for.
    • As jdv noted in his fine answer, there should be a bit of slop in the fit between the bar and the channel, so you'd want to account for that when purchasing the channel. You might even be able to take a miter gauge with you to the shop to try it out on what they have in stock.

As an added bonus, you can help confirm the info in jdv's answer that most of them are standard sizes, or, in disproving it, you can post your own answer indicating that's not the case and help inform the rest of us!

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