# 3/4 Round Corner Gage

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I'd like to know who has made one of these and any tips you would care to share for making one. In the past I have made "special" angle blocks that capture an over all rectangular part at a particular angle. It has a clearance where the edge of the part is located assuring burrs, dings, and chamfers have little or no affect in the location of the edge in relationship to the angle block. This allows me to indicate/probe/touchoff the angle plate/block and use the math to tell me where that edge is. It works, but its cludgy, requires some math (or cad to do the math) when often what I want/need is the location of the exposed edge.

Recently a YouTuber posted a tool they had made. It is basically a cylinder of known diameter with a clearance hole bored down its central axis. Then 1/4 of the round if machined away. When its placed over the exposed edge it can be probed to find center and height of the edge more easily than my previous method. In addition it doesn't matter what angle the work piece is mounted at to find that edge. It should work for most work piece angles of any angle between 90 and 0 where the widest point of the tool is accessible with the probe or edge finder. Of course 90 and 0 would not require the tool.

P.S. Its such a simple elegant solution I am sure the YouTuber wasn't the first one to think of it. Does this tool have a proper name?

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The sort of thing shown here

. I could do with one of those.

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Yep. I was thinking plane round (using some TGP stock on hand), but that's the basic idea.

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Here is another version:

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That looks to be what is being described in this video but another design

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I've designed one of those before for rapid probing corners in flat orientation with a touch probe. Just do a center find routine and you have the corner.

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Is this what you were looking at before

. Although potentially easy to make I'm surprised I haven't seen a commercial offering yet.

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Yeah, that was probably it. I finished making mine and I blew one of the dimensions by more than I am willing to call tolerance. I'll remake it tomorrow.

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Although potentially easy to make I'm surprised I haven't seen a commercial offering yet.

------------------------- Google found "chair" edge finders that use the same principle.

Unless the work blank has been surface ground I zero on the edges of a 1-2-3 block and use however the blank fits against the fixed jaw and end stop as its 0,0 corner. It's at least repeatable.

I found one of these in an antique furniture store for initially grinding a square reference corner.

Sometimes tool boxes show up when he buys estate contents. He saves the woodworking tools for furniture repairs and wall hangers but has no knowledge of or clientele for the pre-CNC machinist tools, except me.

A corner finder made with dowel pins in bored holes would eliminate possible error from a tool change or runout. It should be as accurate as your DRO.

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A chair edge finder and the center corner finder you showed earlier seem to me to be mostly for finding the edge/corner of a rectanguloid work piece clamped parallel to the table. Either in a vise or other clamping setup. The tool in the video link David posted is exactly what I need (and made badly yesterday). Its for indicating in an edge of a rectanguloid that is significantly not parallel to the table. Its not necessarily super precise as the Z height is established by touching off, but an indicator or even a cylindrical indicator can get you pretty darn close with the 1/2 method. I've done it in the past with job specific shop made angle plates and indicated off the angle plate held to the vise with magnets, but it has a couple flaws. If the thickness is variable from piece to piece or unknown I have to take a measurement and do one more piece of math. By using the cylinder on an exposed edge I can just indicate and zero. Further more I only need one for many mounting angles instead of making a new angle plate for every new angle.

Work stop and vise jaw is pretty good for flatish squarish pieces. I've both made and purchased table mounted work stops, and have them for "almost" every mill in the shop. I also have pieces for several more of the articulating variety on the assembly bench waiting on back side machining when I have a chance. I generally prefer table mounted over vise mounted as they can remain in place and move out of the way at the same time maintain "pretty good" part location. Shop blocks get used for so many things I've lost track. One of the most common is making a batch of "identical" molds where it would be convenient to have a consistent thickness from part to part and day to day. I use a 123 block with my height setter on the fixture. The I calculate the final thickness based on the bottom of the part instead of the top. I still have a top zero, but is relative to the fixture instead of the work piece.

There was one of those in the tools, fixtures, etc of my grandfather's that my dad passed on to me. I've only used it once, but at the time it was the only tool I had that would do the job.

Sounds like a great arrangement. I hope he gets front of the line treatment when he needs something machined.

For manual edge finding I usually use the cut and go method or a rotating clicker type edge finder. The clicker gets me close, then I bump out and back slower. I don't know how "accurate" I am with it, but its very repeatable. I can get a higher degree of accuracy with an indicator and a gage block if I need to.

The corner finder like you linked earlier is for electronic probing quickly on the CNC for me, but of course an indicator in/on the spindle or a coaxial would also work with it.

A dowel pin corner tool would be pretty easy to make on the CNC mills. Good enough for wood workers anyway. LOL. The advantage would be they can be made in a single setup reducing tolerance stacking issues.

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When I've sent odd-shaped designs to a machine shop they left orthogonal reference surfaces on the blank as long as possible.

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You're picking on me for saying rectanguloid right? LOL

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Between kintergarden and 1st grade somebody gave me an IQ test. Many years later I was told (third hand) they had never seen a higher score for my age.

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I claim that I got in by lying about my age. My parents wouldn't tell me what my score was. IQ scores never came up in discussions, they were more likely laments about how intelligence alone doesn't guarantee success, or random wanderings as I sometimes do here, perhaps while batting balloons to the kids within the circle.

During economic downturns a large percentage of Mensans were unemployed, and didn't care or need to change our generally frugal lifestyles. One of then was the caterer I worked for at the Renaissance Faire. Another ran a laundromat. I meet interesting and very highly educated people selling stuff at flea markets. The founder of this was previously an aerospace engineer:

common thread seems to be self-reliant independence and unconcern for social status.

I badly twisted my ankle on a joint NH-MA Mensa mountain climb. The person who drove me to a nearby hospital was Head of Emergency Services at a large Boston hospital, but he wasn't licensed in NH. He was upset about being associated with the rustic crutch I had lashed together, though the doctor who saw me camped in northern Canada and loved it.

Congrats, you did it. I would have compared the phugoid oscillation between kinetic and potential energy to tool chatter.

I got into AP classes at the same time as moving to a new school, and found the AP students accepting of outsiders since they were themselves. Theatre people were particularly tolerant since they are very much outsiders. As I was part of the tech crew instead of the talent they put up with my more 'normative' behavior. The contrast with reserved, introverted chemistry students was extreme, and I think a useful exposure to those who act on feelings instead of thoughts, since the script writer had already done the thinking.

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Elon Musk's Twitter activity resembles a pun-filled Mensa discussion.

"What do you call an infinite gear ratio? All torque, no action."

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Anyway, I made the tool. It took me three tries to get one that was marginally okay. By okay I mean its got under 1 thou taper on each face, but its within half thousandth of dimension along its length. That means if I touch off near center it should be within a few tenths. Far better than the clicker I used to locate off of it. 4 of the 8 holes have been drilled. Now I need to touch off and double check center and zero from the other end to drill the other 4 holes. The pilot is a stub length 1/16 (.0625) solid carbide drill. Then finish to size with a longer HSS drill.

I blame the taper on my cheap Chinese mill vise. I probed the bed once and it was a couple thousandths out of flat along its nominal 8 inch width.Most times I use machined step jaws, but for this I set the collet block on the bed of the vise. I figured for the nominal 1 inch length of my tool it would be tolerable. It was, but just barely. Normally I use machined in place step jaws in that vise. Its just a bit to big to fit on my tiny 6x12 surface grinder.

The hard part was measuring it, and its why I badly hosed the first two. A replaceable anvil micrometer might have been able to reach past center, but I don't have one. I tried a caliper but my measurements were all over the place. Finally I did something I do not like doing. I took the collet block out of the vise to measure the flat with a height gage on the surface plate. I don't like multiple setups on parts if its at all avoidable. Every time you put it back you have another chance to screw it up when you screw it down.

I guess next I have to deburr those tiny holes in each plate before continuing on with the next step at the end of paragraph one.

Here is a picture showing the application on the Maker's & Builders group on Facebook. I do not believe you need to log on to see it.Try not to have to big of a laugh at my crazy setup. Okay go ahead. Laugh. The angle blocks turned out to be a good idea. The stack up in the vise had the mold plate off by a full degree from its protractor. Assuming those cheap import angle blocks are accurate. LOL.

... and if you don't trust the hidden tiny url here is the full URl.

If you happen to be on FB, here is the link to it in the group. I do not think you have to be logged in to see it this way either. You do have to join the group to post or comment.

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The hard part was measuring it, and its why I badly hosed the first two. A replaceable anvil micrometer might have been able to reach past center, but I don't have one. ...

---------------- The 1" Mitutoyo Uni-Mike will, the outer edge of the spindle face can be centered on up to a 1" circle.

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Yep, exactly the type pf mic I was thinking of. I would have still had to take the block out of the vise unless I side milled the dimension. Buy end milling the dimension I was able to exhibit my inner cheapness and use a used mill.

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Yep, exactly the type pf mic I was thinking of. I would have still had to take the block out of the vise unless I side milled the dimension. Buy end milling the dimension I was able to exhibit my inner cheapness and use a used mill.

Bob La Londe Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist

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In case my brief description was unclear, it could measure the height (the radius) of a quadrant milled from a cylinder of up to 1" diameter. With the spindle outer edge at the center the toe of the anvil clamping surface just touches a 1" cylinder and clears a 3/4" one. I checked with the center cutoff tool pip of rod stock.

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