What do you think of this build video? Did he take a big risk?

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rkcarguy
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Location: Wa State

Re: What do you think of this build video? Did he take a big risk?

Post by rkcarguy »

Harold_V wrote: Mon Nov 30, 2020 5:58 pm
rkcarguy wrote: Mon Nov 30, 2020 2:30 pm (or if it didn't, you "didn't have it"-according to the owner and foreman).
Need I say more?
Match drilling/reaming with the 2 parts stacked was for hacks lol).
Yes. Hacks. Or those who didn't want to make the same mold (or what ever component) a second time because of a mislocated dowel.
The hack you suggest is called insurance. Why risk failure, when there's a sure-fire way to ensure that the end result is functional?
If you went over, you cranked it backwards and then snuck up on the location again.
That's called dealing with backlash. It's no stranger to those of us who were trained on manual machines, and should be well understood by folks who use DRO's, too, as how the screw is loaded on any machine can spell the difference between success and failure. Those who ignore backlash are asking for problems, even when they use a DRO. Not so much of an issue with a CNC, as the feeds control location, but even they can have problems if the don't have ball screws, or the ball screws aren't tight.

H
The "hacks" part was per them, not me lol. I think the idea was that if we had to replace a mold half that it was ran to the numbers and it would still fit the other mating part. This was a temperature controlled shop that calibrated everything to 2/10,000ths and the ex-military owner was super picky and kept everything spot on. It was a wonderful shop with all the equipment being so cherry and tight, yet stressful place to work because there was no excuses for errors!

Agreed on the ball screws and backlash. The EZ-Trak had ball screws and repeatability was very close, but we did wear out a set hogging alot of stainless with roughing mills. I haven't worked in the trade for over 15 years so a lot of the proper terms have left my memory, whereas the processes and proper ways to do them have not....yet.
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Harold_V
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Re: What do you think of this build video? Did he take a big risk?

Post by Harold_V »

rkcarguy wrote: Mon Nov 30, 2020 7:14 pm The "hacks" part was per them, not me lol.
No problem, and no offense taken. :wink:
I think the idea was that if we had to replace a mold half that it was ran to the numbers and it would still fit the other mating part.
A philosophy I do not share. The last job I held, before starting my humble commercial shop, was owned and operated by nine individuals. Needless to say, in those nine people there were multiple approaches to machining, with no general consensus. One of them, a guy named John Green, took me aside one day and chastised me because I had spent too much time on multiple bronze rollers, parts for an ammunition dismantling tool for the U.S. Army (Tooele Army Depot). It might help you to understand that all I had in the way of instruction was a clipping taken from the print, with no tolerance block included. I had no idea what would be allowed, so I made them per print, assuming a tight tolerance. I was told that he would rather I crash through a job, turning it out in such short time that if I had to do it over (because it wasn't properly made) that there would be ample time left to do so without taking a loss.

Funny. We don't have enough time to do it right, but we have all the time necessary to do it over? That is the philosophy I do not share.

The comment I made about doweling is one whereby there will be no case of error. That's excluding the possibility of a reamer cutting oversized, of course. When one locates dowels this way, they fit, and they fit every time. I NEVER promote a method that offers greater risk of scrap, or of injury. Locating dowel pins is just such a situation.

Consider the fact that dowels may not share the same centerline, thus there's twice the possibility of missing a location. Maybe not a big deal using a diamond pin, but for round dowels, it's an invitation for trouble, even with a DRO. Please note that I did not say it won't work. Sure it will. Until it doesn't.

I too, sought perfection. I have never been intimidated by small or close tolerance work, and, in fact, that was my specialty. I did my level best to use processes that didn't offer the risk of making scrap. In those same years I also did one hell of a lot of tooling, commonly using dowel pins. They were never an issue so long as I used reamers for fits. Location, which is generally never specified, was a non-issue for me, and I chose (random) dimensions that allowed assembly ONLY when the part was properly oriented. That eliminated a fool from dismantling a tool, then assembling it such that it would produce scrap. Simple enough to do---just make sure that the assembly fasteners will align only when the part is properly oriented. You do that by random location of the dowels.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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