# An exercise in frustration, being a hobby machinist



## Janderso (Aug 15, 2021)

I know I’m supposed to make mistakes, I do, all the time.
I’m making some clamps like the Kant-Twist variety.
I am very careful, this is a simple part but it needs to be accurate to +0 -.002”.
I need two pivots, the first one is spot on, OK, piece of cake. I measure one final time, dial in .004” and I turn .010”.
One thing about this project, I’ve never had to turn to a shoulder with this accuracy.
I have to walk away for the rest of the day…….. maybe.
I need to remind myself, it’s OK, you don’t know what you are doing and look what you made.  = scrap?


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## Doug Gray (Aug 15, 2021)

Hang in there Jeff. You'll get it done.


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## Bob Korves (Aug 15, 2021)

We have all been there, Jeff.  "I cut it 3 times and it's STILL too small..."


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## ericc (Aug 15, 2021)

Will the clamp still work with the undersized tenon?  I was wondering if it would bind somehow.


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## Larry$ (Aug 15, 2021)

Bet it will work anyhow. How was the .002 tolerance determined?


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## francist (Aug 15, 2021)

If it's the shoulder to shoulder distance that's off, an appropriate shim would probably allow the piece to function.


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## MrWhoopee (Aug 15, 2021)

Larry$ said:


> Bet it will work anyhow. How was the .002 tolerance determined?


Probably by a freshman engineer (who finally got to ride in front and blow the whistle).


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## MrWhoopee (Aug 15, 2021)

Lucky for you those are some of the simplest parts in the assembly. Wouldn't want to scrap the side plates.


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## Ulma Doctor (Aug 15, 2021)

I have scrapped more parts than I want to admit, but it has taught me to sneak up on critical dimension.
Even though i’m a proficient welder, it’s still easier to take material off rather than put it on.
I often divide the final cuts or make .001” cuts until i hit the mark.
 Since adoption of the practice, there is a lot less cussing and less scrapped parts ,
As you get to know your machines, you are going to know what you can get away with and where you need to slow down 

If this sport was easy, everyone would be doing it!!!
Chin up


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## Aukai (Aug 15, 2021)

Those knob graduations, plus any backlash(if not taken out)drive me crazy, I'm still practicing with the DRO, it ain't infallible either. 
Each part of the line on the knob is wort 5 tenths front of the line, the middle of the line, and the back side of the line it seems


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## Janderso (Aug 15, 2021)

Larry$ said:


> Bet it will work anyhow. How was the .002 tolerance determined?


It’s on the print.
Plus, I want to hit the targets.
This is where you get to know your machine.
In order to measure the spacer, I had to take it out of the collet, determine how much more to cut then try to get the single point tool just touching the shoulder.
I must have got it wrong.
The tolerances are the challenge,fun but frustrating.


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## C-Bag (Aug 15, 2021)

Janderso said:


> It’s on the print.
> Plus, I want to hit the targets.
> This is where you get to know your machine.
> In order to measure the spacer, I had to take it out of the collet, determine how much more to cut then try to get the single point tool just touching the shoulder.
> ...


Making stuff by plans is truly where I found out how much I needed to buckle down.

 In my world missing the dimension doesn’t =scrap. It’s now a future part and I now have some metal tins I keep them in because until I got hip to that fact I was always trying to hunt up those near misses because they would have worked for the project at hand. I also have a tin for machined left overs of various dimensions. That tin is constantly rotating because I’ll need a special spacer for a jig or small part and adding leftovers. 

They are only scrap if they get tossed in the trash. And the sanitation engineers have taken it away.


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## markba633csi (Aug 15, 2021)

Having a crappy lathe helps, cuz then you can always blame the lathe 
-M
"Bad lathe! Now you'll have to stand in the corner till you learn the error of your WAYS"


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## Doug Gray (Aug 15, 2021)

My bins of shame (yes plural). To be fair I was prototyping as well as screwing up.


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## Janderso (Aug 15, 2021)

Doug Gray said:


> My bins of shame (yes plural). To be fair I was prototyping as well as screwing up.
> 
> 
> View attachment 375423


I bought your kit.
The second go went much better.


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## Janderso (Aug 15, 2021)

MrWhoopee said:


> Lucky for you those are some of the simplest parts in the assembly. Wouldn't want to scrap the side plates.


Oh no, we wouldn’t want to scrap the plates. Lots of work here.


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## Doug Gray (Aug 15, 2021)

Janderso said:


> Oh no, we wouldn’t want to scrap the plates. Lots of work here.


Letter stamps to keep the sets , very nice.


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## Janderso (Aug 15, 2021)

I couldn’t end the day with frustration. Now I’m cocky and ready for my next challenge.
These came out within specs.
The larger pins will be drilled and tapped right down the middle, I hope.
The edge finder is a valuable tool.
Made the drilling and tapping a simple step.


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## Janderso (Aug 15, 2021)

Doug Gray said:


> Letter stamps to keep the sets , very nice.


I’m learning


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## Suzuki4evr (Aug 16, 2021)

Aukai said:


> Those knob graduations, plus any backlash(if not taken out)drive me crazy, I'm still practicing with the DRO, it ain't infallible either.
> Each part of the line on the knob is wort 5 tenths front of the line, the middle of the line, and the back side of the line it seems


I must add to your comment. Your DRO is only as good as the amount off wear on the bed,like my lathe, especially close to the chuck,like my lathe and backlash on the crosslide...........like my lathe(need to adjust that).


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## akjeff (Aug 16, 2021)

Janderso said:


> I know I’m supposed to make mistakes, I do, all the time.
> I’m making some clamps like the Kant-Twist variety.
> I am very careful, this is a simple part but it needs to be accurate to +0 -.002”.
> I need two pivots, the first one is spot on, OK, piece of cake. I measure one final time, dial in .004” and I turn .010”.
> ...


Here's a good video on hitting your target diameter. Like most all of Stephan's videos, there's some excellent info to be had. I especially like his explanation on why we shouldn't "sneak up" on a final dimension. Better to divide your cuts so they consistently load your machine the same way, each cut. Made sense to me after he explained it.


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## BGHansen (Aug 16, 2021)

One of the machinist at work was known for the saying, "The sign of a good machinist is how well he can hide his F-ups".  Could you use 0.002" steel shim stock punched like a washer to make up the difference if the shoulder was cut too deeply?

Bruce


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## Dabbler (Aug 16, 2021)

@BGHansen the first line of the saying is "Every machinist makes mistakes.  The sign of a good..."


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## Weldingrod1 (Aug 16, 2021)

In my professional life, if the machine shop -ever- comes back with a problem with tolerance, I always prod the responsible engineer to look at what's ACTUALLY required for tolerance. And then i ask pointed questions ;-)
It's too easy to use the defaults and not your brain!

Sent from my SM-G892A using Tapatalk


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## Tipton1965 (Aug 16, 2021)

BGHansen said:


> "The sign of a good machinist is how well he can hide his F-ups".


Years ago when I worked as a machinist I was talking to an older co-worker.  He said he once worked at a shop that had a pond out back.  He said anytime someone scrapped a part they would just throw it in the pond to hide the evidence.  He said they had a really dry hot summer one year and the pond dried up.  Years worth of scrapped parts were sitting at the bottom.  He said there was even large scrapped castings in there.


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## westerner (Aug 16, 2021)

akjeff said:


> why we shouldn't "sneak up" on a final dimension


I recognize that you are working on OD stuff. Still, Mikey's advice on boring applies here. If you are attempting a cut at less depth than the nose radius of your tool, your results will not be consistent. I have seen it enough times in my hobby shop to make me a believer. 

Rest assured, my scrap/repurpose pile is not small. The lessons learned are absolutely delicious, and my mistakes far outnumber the numbers actually hit.


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## akjeff (Aug 16, 2021)

Sorry for the foulup guys! I edited my post to include the link to the video. CRS strikes again!


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## Doug Gray (Aug 16, 2021)

> The lessons learned are absolutely delicious



Love this sentiment and couldn't agree more!


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## westerner (Aug 16, 2021)

akjeff said:


> Sorry for the foulup guys


No worries. I only quoted your post to illustrate the concept of nose radius/repeatable results. Gazillions of other factors are at play. 
Me too.....


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