Miter bars for Table Saw??

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I am looking to build a crosscut sled for my table saw and want to buy some metal or plastic Miter Bars/Miter Sliders. Any good sources for these. Also, could these be made from some aluminum stock. Looking to fit the standard 3/4" X 3/8" slot. I know you can make these from wood but looking for metal or plastic. Not interested in the expensive Incra ones. -Thanks
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"buck" writes:

some
Just give proper consideration to thermal expansion for either plastic or metal.
Tough to beat white oak or hard maple for this application.
HTH
Lew
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I gotta agree with Lew. Nuthin wrong with oak for runners. I have 3 of the fancy incra ones, they are nice, but really, I do just fine with white oak. Even have one with red oak, I think becuase I had some sitting around that was already the right size. it works too.
I tried poly runners once, they squeezed out so much when I screwed them on, they were un- useable.
-Dan V.
On Wed, 26 Jan 2005 02:58:34 GMT, "Lew Hodgett"

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Dan Valleskey <valleskey at comcast dot net> wrote in

Lew and Dan are right. The oak and/or maple beat the metal ones hands down.
But, if you're not convinced, you can buy the Delta miter guides at Rockler, like I did. Then you can remove them, put them on the shelf, replace them with oak, and wish you had the $20 back that you spent on them. Like I did.
It's not like they are more convenient. The great thing about wood is being able to put the screws in from through the sled top, and not having to hit a threaded hole, blind.
Gets you back to woodworking much more quickly.
Patriarch
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On Tue, 25 Jan 2005 22:26:08 -0500, Dan Valleskey <valleskey at comcast dot net> wrote:

HDPE is OK, but UHMW or Teflon is trading a little hoped-for slipperiness for far too much loss in mechanical stability.
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Well, if you do it properly - no. Counterbore, spread the load with the proper fastener.
The aluminum ones have elaborate but inadequate means built in to do squeeze the sides, and it's considered an advantage.
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Is there really a significant difference in thermal expansion rates for plastic or aluminum vs. cast iron? Granted, the bar will get wider as it warms up, but so will the slot. Does it *really* make a difference?

And what about expansion or shrinkage driven by changes in moisture content? That's gotta be at least an order of magnitude greater than any thermal changes in dimension, and obviously does not affect plastic or aluminum.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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Doug Miller wrote:

I doubt that thermal expansion is a significant factor over the likely temperature range. Expansion/contraction due to humidity changes can be a far more significant problem with wood.
However, if you use a typical sled construction technique employing both mitre-slots with a wood sled the dimensional changes in the sled itself (due to humidity changes) cause much more trouble than the sliders by grossly changing the distance between sliders. Particularly as the sliders are usually constructed of relatively stable hardwood and sealed/waxed whereas the sled usually isn't.
If you live in a climate that is dry as a bone in Winter and humid as all get out in Summer it can be a serious problem.
One with experience (I built my sled in Winter - it's unusable in Summer). (:-)
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wrote:

I do see significant thermal expansion in the rails of my table saw. it's enough that I can't trust the scale on my biesemeyer. now, that's a lot more metal than a miter bar, but it's real. OTOH, the baltic birch ply sliders on my sleds don't give me any problems with humidity changes.

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snipped-for-privacy@all.costs wrote:

Well, to be fair the thread was on mitre bars and I was commenting on the expansion of the significant (3/4") dimension but lets see:
The thermal expansion coefficients:
steel is ~ .000006 in/in/degF aluminum ~ .000012 in/in/degF UHMW ~ .00011 in/in/degF wood     ~ .000003 in/in/degF (cross-grain) **
(** I found several references for this suprisingly small value for wood - less than steel. It seems to confirm that the major problem with wood rails would be humidity rather than thermal expansion).
So for a 3/4" mitre bar over a 30 degF temp. range the expansion would be:
steel = .000135" (.000006 x 30 x .75) aluminum = .00027" UHMW = .0025" wood = .00007"
For a cast-iron/steel table, the diferential expansion of the bar to slot would be:
steel = 0" aluminum = .000135" UHMW = .0024" wood = .000065"
For an aluminum table, the differential expansion would be:
steel = .000135" aluminum = 0" UHMW = .0022" wood = .0002
Over this temperature range, I would suggest that only UHMW *might* (just barely) be noticeably affected by thermal expansion/contraction. (I still feel that humidity would be the controlling factor for wood. I don't offhand have any hygroscopic data for UHWW ... some plastics - nylon for instance - absorb a fair amount of water and can swell noticeably with humidity changes).
As far as your front rail goes, assuming it's ... what, 4 ft long? The expansion in that case (over the same temperature range) would be:
steel rail = .0086" aluminum rail = .017"
I assume the scale is thin and bonded to the rail so the rail would control the expansion. I'm not familiar with the Biesemeyer so I don't know the material for sure but the expansion is almost 20 thou for aluminum (but over the total length ... proportionally less for shorter distances). Whether that's a problem in your work, only you can say. (I think, in my case, my innate lack of craftsmanship would swamp it (:-) ).
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wrote:

the rail is about 6' long. and I live in Arizona. I'll figure the shop temp varies close to 100 degrees from a cold day in the winter to a hot day in the summer. that would result in a total variance of .043, or about 3/64".
I'm definitely seeing more than that, so there's probably something else going on. for instance, right now it's reading about 1/16" short in the 36" range. it's not particularly cold weather right now- brisk, but nice.
hey, and thanks for digging up those numbers.
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snipped-for-privacy@all.costs wrote:

Is that all? My shop temperature in the mountains of Virginia varies by about 120 degrees from the lowest low to the highest high, as measured by the thermometer inside the shop. (Not by ambient air temps.) A lot of this is because it gets hotter than my thermometer can actually tell me in the summer. I've gone out there on a 20 degree day and seen it 55 inside the shop, just from solar heating. I really need air conditioning, but I'm not going to get it. :(
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snipped-for-privacy@all.costs wrote:

One other thing that is going on is that the rail is tied to the table at several points so they fight with each other during expansion. The table will probably win so the rail will try to compensate by distorting (bowing or twisting). I wouldn't have thought that would be enough to give you the effect you're seeing .... but who knows?

You're most welcome. It was an interesting exercise (for me).
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buck wrote:

Your local woodworking store? Lee Valley sells UHMW which fits. www.metalsupermarkets.com might be in your area. ebay (search for aluminium or aluminum, or UHMW)
I use MDF with an edge of scrap arborite for smooth running. It may be a few thousandth's wider than .750, but a belt sander, plane, router, or jointer will fix that.
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I would think waxed hard maple would wear better than aluminum or plastic. I got a 3ft sample of 4" wide 3/4" maple flooring for $2 and it'll provide enough runners for a years worth of jigs and sleds.
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I just built one with UHMW runners from Lee Valley. They was a little play in them when I set them in the miter slots of my Delta Contractor saw, but once they were screwed to the sled base, I had a nice fit.
FYI, they were selling these all over the place at the Indy woodworking show this past weekend, so if there's one coming to your area soon, you might pick them up there. Otherwise, hard to beat Lee Valley.
I almost bought the metal bars at Rockler, but was easier to drill and screw down into the UHMW from above. Word of caution - screw once in each end first, don't draw lines on the sled base of where the miter slot should be and screw between the lines. YOu could miss the rail and have the screw ding the miter slot. DAMHIKT...
buck wrote:

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Never had a problem w/ UHMW. Got a load from a buddy of mine and been using it w/ no problems.
Check ebay for some - should be able to get it pretty cheap.
OR just maple or oak scraps.

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I'm afriad I have to be the voice of decent. I've tried oak, maple and other hardwoods. They work great to begin with but if you make them to have a good, tight fit, I discovered that weather does have an effect and they weren't always smooth over time. I also tried the UHMV thing and found the same thing as the others. Once they were screwed, they splayed out making it difficult to get a good fit. I reamed out the hole and got a workable solution but I found a better way. Incra makes slot runners that have built in slop adjusters. You will spend about $20 on an 18" one but it was well worth it to me. It was adjusted to fit tight and it slides like butter regardless of the weather. It aslo has the holes predrilled - for something I use so much like a crosscut sled, the $20.00 was dirt cheap.
Don

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wrote:

FWIW, I have used UHMW and I have used my brad nailer to attach pieces to my MDF sleds. No spreading. When I have used screws, I have made an over-deep tapers for the flatheads and sneak up the tightening on the screws. I have actually found that by tightening/loosening the screws I can adjust the fit, as needed. -- Igor
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some
looking
Cutoff has the white UHMW, works fine. Miter sled has leftover mdf-filled Pergo-type flooring on it, also fine. I'm in a basement, and the climate is cold, so wood doesn't work as well for me. The EMC gets up 15% in the summer, 4% in winter. Don't waste your money on the adjustable aluminum. Or if you care to, pay the postage and I'll ship you one that is on my circle-cutting jig, so I can replace it with one of the others.
First time you get some moisture together with that oak strip you forgot and left on the saw and your iron top, you'll regret it.
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