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Measuring Internal Angles

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SamI

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Hi Guys,

As some of you may know from other threads I am in the process of refurbishing a collet closer and modifying to fit my lathe. To do this I need to reverse engineer a part. What I've got stuck with is the measurement of this angle:

287062

Now the angle isn't critical so in practice I could probably just guess however I would like to know how to measure it properly for future reference. As it is I currently have some modelling clay setting in it figuring that I can use an angle gauge to determine the angle however I would prefer a direct method of measurement for convenience. Another thought I had would be to chuck it up, offset the compound and run an indicator on the angle but again I would be interested in other methods.

So, how would you measure this?
 

Canus

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With the dimensions you have provided on your drawing there is no way to calculate the angle. If you can get measurements of the base and height of the desired angle a trig table can be used to determine the angle.
 

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SamI

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I have the physical part that i am trying to measure rather than to find the dimension from the drawing. On the existing part there is a radius at the bottom so it is difficult to measure the base length so I was hoping for a way, if possible, to measure the angle directly.
 

Cadillac

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Do as you said. Set up on machine and dial in your angle directly. Will be as accurate as you dialing in.
 

SamI

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Thanks all for the suggestions. Looks like the dial indicator is the way to go!
 

macardoso

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If the part is taken off the machine it is tricky to measure. When I used to work in inspection we would melt a stiff green metrology wax stick and press it into the inside features. Once removed it would carry the shape of the internal feature. We would usually then set the wax up on a optical comparator and measure the angle that way. Not stuff your average homeshop would have, but still an interesting solution.
 

Jimsehr

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If you are drawing the part on a cad program. The program should tell you the angle.
 

SamI

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If the part is taken off the machine it is tricky to measure. When I used to work in inspection we would melt a stiff green metrology wax stick and press it into the inside features. Once removed it would carry the shape of the internal feature. We would usually then set the wax up on a optical comparator and measure the angle that way. Not stuff your average homeshop would have, but still an interesting solution.
Sounds like a high tech version of my modelling clay method! The plan is to take the clay and use an angle gauge to determine the angle. Luckily for this part the angle is not critical and as long as I'm within a degree or two I should be alright.

If you are drawing the part on a cad program. The program should tell you the angle.
The problem is I don't have enough information to determine the angle. I only have one leg of the triangle and have no means of measuring any of the others so while Inventor can give me an angle it is meaningless until I can determine at least one other feature.
 

Jimsehr

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You could come real close to checking size by using some kids clay ,you can get at Walmart.
 

Chewy

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If I may add my 3-1/2 cents. You already have all the information you need to solve the problem with the equipment you have on hand. The answers given above are all correct. You just need to solve the problem. You need a lathe, a test indicator mounted to crosslide/compound and a chuck to hold the part.
If you are not familiar with Advanced Innovations, Austen Texas, here is a link to one of his videos:
. It tells how to use a ball to determine depth of chamfer. That is not what you are doing, but it is one of a series of videos telling how to use math to solve a problem. The math comes down to using a right triangle to solve problems. I started a couple of weeks ago inventing and solving problems just like yours. Blame Joe, it got addictive.

You have the base of the triangle (b) which is .65. your drawing looks like a 30/60 triangle. Entering the following information b=.65 B=30 A=60 gives the following dimensions:a = 1.126   b = 0.65   c = 1.3. c is the length of the angle cut. Don't shoot the messenger. I just used your drawing and one dimension as an example. Go to https://www.triangle-calculator.com/. there are several formulas that are available to go with different information that you might have. I used Triangle Calculator for this one. Each time you calculate you get a picture so you know if you did it wrong.

Mount your piece in the lathe, concentric, TIR etc. Put a piece of square stock in tool holder, insert next to angle and dial compound/crosslide until it is the same angle. Switch to test indicator and run back and forth on angle. Adjust crosslide for 0 deflection on gauge just like doing a taper. Read crosslide and plug in degrees in formula. Done! Down and dirty, easest and quickest.

Alternate. Use test indicator like an edge finder. touch inside front edge, back out and at point it changes, set 0 on leadscrew. Advance inside and do the same. At point reading changes, read numbers on dial. Account for backlash. * Important!* you have to look at how the dial indicator is touching. If you take readings off of center high point, your good. If you use the side/thickness of ball add 1/2 diameter just like an edge finder.

You said you have a chamfer inside edge. Your options are to guess. Ignore it. Get really fine readings with the test indicator and do the math. Or take a cast and use dial indicators, feeler gauges and small drill bits and really good eyeballs to increase the accuracy of your readings.
Don't know about green metrology wax, but I do know about lost wax casting jewelry. You can buy the wax to make ring and jewelry patterns, but you don't need that much, got an oz from a jeweler who makes his own. Make an aluminum foil dish or cupcake sided holder. Turn on oven to 350 and put inside. Check every few seconds until it looks liquid. The wax melts between 150 -350 degrees depending on brand and properties.

Prepare the piece. Spray cooking oil on area. PAM or something like it. You want to pour the wax so you have a narrow width and a thick vertical piece. Make a trough front to back with anything that you can and pour wax. Let cool to room temperature and remove by rocking side to side, not by prying up. The wax can be filed, drilled, built upand measured to determine/adjust chamfer or edge rounding. Again, take into account thickness, diameter or distance and adjust calculations. If you really try hard, you can get down to 1-2 thousands in your calculations.

Sorry about the length. All the answers above were right and I have used all of them depending on what was easier at the time. Good Luck!
Charles
 

tq60

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If in the lathe you can use a sharpie to ink it up.

Next while running get a point like paper clip or compass point touch the face of the taper at 2 points.

Not with calipers measure the distance between 2 and that is the length of angled side.

Now difference in diameters and 1/2 that becomes the short side of triangle.

If you need long side place bit in tool post and touch one then caliper to measure to other.

Now set compound and turn scrap and test fit until it properly wipes off the ink.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
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