Shopsmith Forums

I'm not going to attempt to explain. I just know my MiterSet does what I expect of it. What ever the incorrect numbers are, here are some of my measurements.
The MiterSet works well and there is no wiggle room for the Shopsmith miter bar.

Dusty,

Only thing I can think of is there "might" be an issue with inside versus outside measurements with your calipers. On the surface, that is the only thing different between all of your measurements, i.e. one side of caliper is measuring inside the miter slot and other side of caliper is measuring outside of miter bar. Is it possible there is some fixed offset in your calipers for inside measurements that is causing it to be lower than actual?

It looks pretty straight in your pictures, but also if you were at an angle measuring inside dimension then the measurement would be smaller than actual. Conversely, the outside measurement, if taken at an angle, would be larger than actual. I don't really see this in the your pictures that I can tell, i.e. the calipers look straight and aligned with what is being measured.

RFGuy wrote: ↑Thu Feb 25, 2021 3:26 pm Dusty,

Only thing I can think of is there "might" be an issue with inside versus outside measurements with your calipers. On the surface, that is the only thing different between all of your measurements, i.e. one side of caliper is measuring inside the miter slot and other side of caliper is measuring outside of miter bar. Is it possible there is some fixed offset in your calipers for inside measurements that is causing it to be lower than actual?

It looks pretty straight in your pictures, but also if you were at an angle measuring inside dimension then the measurement would be smaller than actual. Conversely, the outside measurement, if taken at an angle, would be larger than actual. I don't really see this in the your pictures that I can tell, i.e. the calipers look straight and aligned with what is being measured.

Absolutely ! Taking accurate measurements with a pair of calipers requires some technique. It is also possible that these calipers may make a contribution. They are not like the ones I used to seen to PMEL every 6 months. Calibration...what calibration.

Bottom line...MiterSet is not IMO the root cause.

I have a set of setup blocks from WoodRiver, a Digital Caliper from Wixey (WR100) and a Digital Caliper from Huskey. Using these to validate performance of the tools and of myself I find that deviations in third decimal position are not only possible but very likely. Repeated measures made that obvious. Even when measuring nice smooth set up blocks with the same caliper I saw deviations.

Good thing I'm not a machinist.

dusty wrote: ↑Thu Feb 25, 2021 4:23 pm Absolutely ! Taking accurate measurements with a pair of calipers requires some technique. It is also possible that these calipers may make a contribution. They are not like the ones I used to seen to PMEL every 6 months. Calibration...what calibration.

Bottom line...MiterSet is not IMO the root cause.

I have a set of setup blocks from WoodRiver, a Digital Caliper from Wixey (WR100) and a Digital Caliper from Huskey. Using these to validate performance of the tools and of myself I find that deviations in third decimal position are not only possible but very likely. Repeated measures made that obvious. Even when measuring nice smooth set up blocks with the same caliper I saw deviations.

Good thing I'm not a machinist.

Dusty,

I think you missed my point. According to your measurements the miter bar should NOT fit in the MiterSet slot you have (smaller width slot than miter bar width). Even if your caliper measurement is off/inaccurate it should be a fixed offset, in theory, that should apply to all of your measurements. In other words, I would expect all your measurements to be off by the same fixed offset, but this doesn't appear to be the case. The fact that you have a smaller measurement on the slot than the bar makes no sense. The caliper has two sets of jaws (upper and lower)...one clamps down on an object (O.D.) and the other expands to fill an opening (I.D.). What I was wondering is if perhaps your calipers have a problem with inside measurements (upper caliper jaws). This could be from excessive wear on the jaws, possibly a different zero cal is required for each jaw set, faulty electronics, etc., etc. I was trying to think of a way that perhaps this could be checked/tested, but I haven't been able to come up with anything to check the jaws against each other. I guess one test perhaps would be to measure the miter bar at its thickest point and while doing it tighten the locking knob on the caliper at that width. Then try taking the caliper and see if the upper jaws will still fit in the MiterSet slot. If so, then it proves you have a measurement problem, i.e. there is a disconnect between the upper versus low jaws on your calipers. They should match for inside versus outside measurements.

I am not a machinist either but based on your pics, I think you did a good job of holding the calipers as square to the MiterSet and miter bar that you can so I don't think it is the source of error.

On my cheap caliper the outside measuring jaws when closed yields a thin amount of light coming through the top, inside measuring jaws. This means that the inside will not read correctly when the lower, outside reading jaws are zeroed. When I try to quantify the amount I see about .003". This is only an approximation based on me visually looking for the light to vanish between the points. So when I do inside measurements I either re-zero at this location or normally just add the .003" to the measurement. I have two of these Pittsburgh ie Harbor Freight units and the one mentioned is the worst of the two, it is also the older one. I still use them for woodworking but if I were wanting some thing more accurate I'd pull out the better ones I have. Just don't like to think about dropping a $170 one on the concrete when I don't have to chance it.

I've been to lazy to get out my expensive calipers to verify this number because well I've been to lazy...... Maybe this spring??

Ed

So now I felt motivated to check this out a little farther. It seemed like a simple way was to simply use a feeler gauge to see what the space was. Started at .002" fit easy, then went to .004" and it was a no go. So there you go my guess at .003" was right on, looks like I still have it.....

And yes as required here is the picture:
Ed

Game Set Match goes to reible ! :-)

RFGuy wrote: ↑Thu Feb 25, 2021 3:26 pm Dusty,

Only thing I can think of is there "might" be an issue with inside versus outside measurements with your calipers. On the surface, that is the only thing different between all of your measurements, i.e. one side of caliper is measuring inside the miter slot and other side of caliper is measuring outside of miter bar. Is it possible there is some fixed offset in your calipers for inside measurements that is causing it to be lower than actual?

It looks pretty straight in your pictures, but also if you were at an angle measuring inside dimension then the measurement would be smaller than actual. Conversely, the outside measurement, if taken at an angle, would be larger than actual. I don't really see this in the your pictures that I can tell, i.e. the calipers look straight and aligned with what is being measured.

What will demonstrate if I measure a set up block (known dimension) with a pair of calipers (inside jaws) and then with a different set of calipers measure those outside jaws. In a perfect world - all measurements would be identical - right?

Go one step further and use each caliper to measure the other caliper - inside to outside and outside to inside. Again, all measurements should be the same.

Turn the calipers off (they self zero with the jaws open when turned back on). Now close the jaws of both calipers. Perfect measurements will result in identical readings equal to the original setup block. Any reading other than identical indicates deviation somewhere.

I would hope for no deviations at the third decimal.

Ed,

Good tips on caliper use and inside measurements. Thanks for the suggestions. The lowest feeler gauge that I have is 0.0015" and it would not fit in between my inside measurement jaws if inserted straight on (orthogonal). At maybe a 45 degree angle it slips through, but not when attempting to insert it straight. Of course, this is a more expensive caliper set so it probably has a smaller gap than the less expensive one you checked. Not knocking the cheaper calipers and I get their appeal. I am always extra careful when I take my only set of calipers out of its case. I hope I never drop them since it took me decades before I broke down for this particular tool purchase.

Dusty,

I am not a machinist and was only offering a suggestion for investigating the discrepancy. If it were me and I had a measuring device in my shop like your calipers I would throw them in the trash. If you can't explain why your inside measurement has an offset and can't correct for it like Ed suggested then it will lead you astray one day with a measurement error. We are not in a perfect world and in this imperfect one, a miter bar that is wider than a miter slot will NOT fit, yet somehow it does in your shop.

dusty wrote: ↑Fri Feb 26, 2021 4:29 am

RFGuy wrote: ↑Thu Feb 25, 2021 3:26 pm Dusty,

Only thing I can think of is there "might" be an issue with inside versus outside measurements with your calipers. On the surface, that is the only thing different between all of your measurements, i.e. one side of caliper is measuring inside the miter slot and other side of caliper is measuring outside of miter bar. Is it possible there is some fixed offset in your calipers for inside measurements that is causing it to be lower than actual?

It looks pretty straight in your pictures, but also if you were at an angle measuring inside dimension then the measurement would be smaller than actual. Conversely, the outside measurement, if taken at an angle, would be larger than actual. I don't really see this in the your pictures that I can tell, i.e. the calipers look straight and aligned with what is being measured.

What will demonstrate if I measure a set up block (known dimension) with a pair of calipers (inside jaws) and then with a different set of calipers measure those outside jaws. In a perfect world - all measurements would be identical - right?

Go one step further and use each caliper to measure the other caliper - inside to outside and outside to inside. Again, all measurements should be the same.

Turn the calipers off (they self zero with the jaws open when turned back on). Now close the jaws of both calipers. Perfect measurements will result in identical readings equal to the original setup block. Any reading other than identical indicates deviation somewhere.

I would hope for no deviations at the third decimal.

That’s what I do, Dusty. Except that I use a micrometer instead of the second set of calipers, because that’s what I have.

My second-hand Mitutoyo dial calipers are off 0.003” between the inside and outside measurements. Someday, I’ll have them repaired/recalibrated. For now, I just compensate by adding 0.003” to the inside measurements.