Thread: Taking the slop out of your mitre slide.

Yeah, like we've all got a, relatively, large diameter of phosphor bronze rod hanging around Bob, and it's so easy to get. Gunmetal would work as well and because it has a lead content should provide a nice sliding action, a bit easier to come by too. Certainly hard enough wearing to do a good job.

Of course you could buy one of the commercially available mitre bars that have nylon adjusters already fitted. They're pretty cheap.

Nice job though.

Phosphor bronze is actually quite easy to obtain and also not that expensive.
I got mine from George White | Australia's leading stockist & distributor of non-ferrous metals in clayton and it cost $16 for a 200 mm long x 20 mm diam rod.
I could have asked for a shorter piece but I needed some for another job so I killed two birds with one stone.
I would not use gun metal or nylon for this purpose as they are both too soft (eg Phosphor bronze is about 2.5 times harder than gunmetal.) and depending on use would need repeated adjusting.
The ideal material for the cams is one that matches the hardness of the cast iron table


Probably the greatest difficulty for a woodworker with little of no MW gear is creating the flat bottom recesses in the slide.
However, the recess does not have to be circular it could be all the way across the slide and could even be done with patience with a hacksaw and file.

Originally Posted by BobL

I would not use gun metal or nylon for this purpose as they are both too soft

The contact patch of your phosphor bronze is very small and it will quickly wear, the 'matched' hardness of the materials will make no difference your PB will wear out in the short term while the cast iron will last forever. The nylon is split and can be rotated to bring a new surface into contact with the side of the mitre slot. I'm confident that the one's I have will comfortably outlast me. If you really want a hard wearing bronze try manganeze aluminium bronze.

You've done a nice job, but I think you've wasted your time. But whatever!

Originally Posted by aldav

The contact patch of your phosphor bronze is very small and it will quickly wear, the 'matched' hardness of the materials will make no difference your PB will wear out in the short term while the cast iron will last forever. The nylon is split and can be rotated to bring a new surface into contact with the side of the mitre slot. I'm confident that the one's I have will comfortably outlast me. If you really want a hard wearing bronze try manganeze aluminium bronze.

You've done a nice job, but I think you've wasted your time. But whatever!

Manganese bronze is too hard and will wear the CI slot.

It sounds like you've missed the whole point about the phosphor bronze (PB) discs having an offset centres, so just like your nylon pieces they too can be rotated to a new contact patch when the existing PB contact patch wears but I will bet mine will wear far slower than your nylon ones. The difference in hardness between nylon and PB is about a factor of 10 so I will only have to adjust mine about 10 times less than yours. I had wide range of plastics in my stash I could have used but I have a 40 years of experience with using plastics in a workshop and laboratory environment, besides poor wear characteristics plastic also stretches, warps, and cracks, which I why I went for the PB.

The material is actually not that important, if someone doesn't want to spend the dough on the PB they can pretty much use anything softer than the CI table as long as they are prepared to adjust more often and if required to replace the discs . As it was I made up 2 spare PB discs, not because I expect to ever wear them out but because I might lose one.

Aren't bearing parts like these supposed to be sacrificial? The idea is that they protect the surface they're bearing against from wear and damage, isn't it? If both materials are of equal hardness then they'll both wear, won't they? Over time and after several adjustments you will no longer be able to use the mitre bar in the other slot on the table without first having to adjust it.

Early last year I bought some mitre bars. They're 650mm long, have five thickness adjustment rings and a removable fitting at each end for undercut mitre slots. They were also supplied with spare adjustment rings. They are long enough to be cut to make two separate bars if required. They were $27.30 each delivered. A much better option IMO.

Yes I'm sure your PB will last longer than my nylon, but my mitre slot will last longer than yours and remain true. So I'll always have the option of using a replacement mitre bar that will work equally well in any mitre slot on any of my machines. You have done a very nice job. Unfortunately the premise on which you based your choice of material is totally flawed.

Originally Posted by aldav

Aren't bearing parts like these supposed to be sacrificial? The idea is that they protect the surface they're bearing against from wear and damage, isn't it? If both materials are of equal hardness then they'll both wear, won't they? Over time and after several adjustments you will no longer be able to use the mitre bar in the other slot on the table without first having to adjust it.

This is counteracted by the fact that the disc represents a small contact point wearing against a much much larger area of the slide slot. So after the disc has worn 0.1mm the slide will only have worn 0.001mm The idea of using equal hardness sliding components is very commonly used in mechanical engineering.

Yes I'm sure your PB will last longer than my nylon, but my mitre slot will last longer the yours and remain true. So I'll always have the option of using a replacement mitre bar that will work equally well in any mitre slot on any of my machines.

Don't forget the other side of your steel slide is also wearing on the insides of the slot and there is a much larger contact area involved so you will still get slot wear - probably about the same amount of slot wear I will see.

Originally Posted by BobL

Don't forget the other side of your steel slide is also wearing on the insides of the slot and there is a much larger contact area involved so you will still get slot wear - probably about the same amount of slot wear I will see.

On the opposite side of the bar to the adjusters the contact is full depth and there is full contact between the side of the bar and the side of the slot so the wear is virtually non-existent. As far as that wear point is concerned there is no difference between either of these alternatives or indeed any other system, I don't know why you even bothered to raise the issue. Unless it's to distract from the real issue at hand and see you standing on firmer ground?

I agree to disagree.