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|12-12-2018, 02:42 AM||#1 (permalink)|
Mad Science of Paintball
Join Date: Jul 2011
Fixing a repair... or maybe repairing a fix?
They say you can tell how experienced a machinist is by how well he fixes his mistakes. It's also been said you can tell how experienced a machinist is by how well he hides his mistakes.
Thankfully I'm experienced enough that I don't make too many mistakes these days- at least, that I'm gonna tell you lot about - but I'm also experienced enough to know I sure as hell ain't perfect, and that as soon as I let my attention drift, something is gonna get screwed up.
In this case, I made TWO mistakes on the same project, eventually spending almost five hours on what was billed as a $45 job.
And you guys wonder why I'm not rich.
Our story begins with a customer with an Autococker SR body. The SR was an attempt by a bought-out-and-corporate-rebranded WGP to make the Autococker keep up with the then-new wave if inexpensive electros about a decade ago. They were, as I recall, made in China (or at least overseas) and wound up with a poor reputation for reliability- the electronics in particular had a near-100% failure rate after a couple of years.
My customer, however, was looking to convert his SR body over to either a pump or a mechanical semiauto build. And do to so, he wanted the "full size" body cut down to a "MiniCocker" size, and the original not-standard-to-any-Autococker 1/2"-20 front block bolt retapped to standard post-2000 9/16"-24 front block thread.
That's normally an easy and fairly quick mod, and I usually only charge about $45 for it. It's worth noting that I've been charging that same price for the mod for at least fifteen years or more- I should have raised my rates a long time ago, but as costs went up, so did my speed. Today I can do the same mod in a fraction of the time it used to take me a decade ago.
And you guys have wondered why I've wasted so much time on rebuilding all these machines.
This kind of mod is easy. These days I'll just bandsaw off the bulk of the body extension, plunk it in the mill vise, mill the stub down to length (made even easier these days with the DRO on the mill) then set it vertically in the vise, indicate to the existing hole, bore if necessary to .515" or so, tap with a guide, deburr, clean, and mail.
And, of course, that's exactly what I did on this SR body.
Now, the problem comes in due to the fact that I wasn't terribly familiar with the SR. I've only had a couple in the shop before, only one got dismantled, and both of them were roughly a decade ago. The only thing unusual I noticed about the front block bolt back then was the nonstandard size. So I of course assummmmed that like very single other Autococker in the entire known universe, the front block bolt hole was in fact centered on the body.
As it turns out, it is not.
Apparently in order to make clearance for the SR's funky intergrated-LPR front block, they offset the mounting bolt roughly an eighth-inch to the side. And naturally I did not notice this until the job was done and I was deburring and cleaning everything. That was mistake number one: Had I noticed, I'd have been able to rebore the existing undersize hole in the right place, tap it, and in all likelihood all would have been well.
I contacted the customer and let him know what's up. If he could still make the build work as-is, I'd send it along at no charge. But he, not surprisingly, wanted it properly fixed, so he of course wouldn't have to deal with headaches like custom-bent pump rods or possible 3-way linkage issues.
Okay, so I've got to fix this. The standard technique for fixing a stripped or damaged hole in an aluminum body- without the issues that TIG welding would incur- is to drill and tap it out larger, permanently affix a new aluminum sleeve, and then redrill and retap for the original thread. I do this all the time to fix Autococker grip frame screw holes, to close up "eye" holes, and patch grip-frame bottomline holes.
Now, the issue here is that while I can bore the hole in the mill, any tap used to recut the threads to a larger size would be far too coarse. The "replacement" threads would then cut through the root diameter of the outer threads. The solution to that little conundrum is to cut custom threads on the lathe. I can make the threads any diameter I want, and as fine as I want, custom-fitting it to the situation at hand.
Now, the problem to that solution is holding the body in the lathe. The SR body is heavily milled and there are few flat, true or square surfaces anywhere, save for the grip frame mounting face.
After a bit of pondering, I decided to go the easy route. I found a chunk of 3/4" aluminum round bar in the bins, and turned a length of it down to .690".
The body then simply slips on like so.
I'd originally envisioned threading the end to 5/8"-18, and have the arbor screw into the valve nut threads, but the SR uses a slide-in valve, like a typical blowback clone, so a simple straight rod worked just as well.
To retain the body, I simply marked out the location of the valve locking setscrew, and filed a flat on the arbor.
The body is then just slid into place, and the set screw cinched down on that flat. (The flat also keeps the setscrew from raising a burr that would make it hard to remove the body later.)
Now, this produces a LOT of overhang, plus an imbalanced load, so I couldn't turn it too fast, and I had to take a lot of fairly light cuts just to make sure I didn't stress anything too much. But, with a little patience, I was able to start turning the offset hole back to round.
The plan here was to turn the offset hole round, thread it to a very fine pitch (like 32 TPI, maybe) then turn a custom plug that could be loctited in and rethreaded to the proper front-block thread.
And of course here was my second mistake:
The turning was going just fine, but I soon ran into a problem. I had again asummmed I had the room to turn the hole round. But I hadn't yet cleaned out all the old threads, and was in fact quite a ways from it, when I was already getting dangerously close to this groove feature milled into the body. There was no way I was going to be able to clean out all the threads, and NOT break through that milled channel.
I considered going ahead and threading the chamber anyway, I should have had enough meat for a shallow 32 pitch thread, but I wasn't sure the old coarse threads would seal with just Loctite. That meant getting out the fabled JBWeld epoxy, which from past experience doesn't play well with fine threads.
So, I had to go with a different fix to fix my fix.
I turned up a snug-fitting plug to go in the as-is turned hole, with the bore roughly drilled out, and a couple of shallow grrooves around the outside.
I then used a small slotting saw in a Dremel to make some shallow, rough notches inside the bore, both to give the epoxy something to mechanically "key" to in addition to the chemical bond.
Then, using the bottom of a handy spray can out of the trash, I mixed up some JBWeld...
Smeared both the bore and the plug liberally...
And stuck 'em together.
Once the epoxy had cured for about 24 hours, the rest was back to a standard turning job, apart from having to take light cuts and at a relatively low speed, due to the excessive unsupported length of the job.
Carefully turn the face down...
Bore the chamber to size...
And, to keep from putting too much stress on the epoxy by trying to crank a tap into it, I carefully single-point threaded the boss, even though the spindly arbor was not particuarly happy about it.
Leaving it slightly undersize, I finished it off by then running the tap in, which just cleaned up a little bit of the thread form to make it spot-on. Note the wooden brush handle up against the compound to keep the body from turning while I ran the tap in.
Check it against one of my Flattop bolts to make sure we're good...
And deburr, scrub, rinse and dry, and we're done.
It's kind of a shame I can't charge the customer when I mess up- that would have been about a $200 mod.
|12-12-2018, 03:04 AM||#2 (permalink)|
Voted most ball-fondliest
Join Date: Aug 2012
Location: Calgary, Alberta
Great writeup, thanks for sharing! I have a few projects of my own I wanted to do which would require mounting a body on an arbor like that. "Am I crazy, will that even work?" I used to think. It's nice to know everything has been done before, lol.
|12-12-2018, 03:06 AM||#3 (permalink)|
Join Date: Nov 2016
Location: Santa Rosa Ca
This sir is why you are the king of the mechinest world Atleast in my book (the cool comics also help . )
Still a broke college student
The odder the better
My pb colllection is worth more than my car but you know life choices
|12-12-2018, 03:20 AM||#4 (permalink)|
Join Date: Jun 2009
Location: victorville ,Cali
Very, very clean.. Beautiful!
Ebay, camocow200 (1400) + 100% positive feedback
darr_musi (850) + 99.9% Positive Feedback
MCB (350) + 99.5% positive feedback
|12-12-2018, 03:37 AM||#5 (permalink)|
Join Date: May 2012
I've always hated the Sr. Only worked on a few but all of them have been a huge pain
^^^ If you are new to the sport and need help finding gear, click here!!!^^^
|12-12-2018, 03:40 AM||#6 (permalink)|
Join Date: Apr 2011
Location: Portland, OR
Thorough integrity. You deserve an accommodation and a firm handshake. And probably $200.
You gave both a candid and well-documented walkthrough of what went wrong and how to fix it. Many lesser experienced mechanics have plenty to take note of here, despite your humble approach to outlining your mistakes.
We all make mistakes. Few of us possess the capacity to admit it, document it, and explain the solution you came up with. And for that, I thank you, and do honestly appreciate this.
I may never be presented with this, ever. However, I now know this about the Trilogy's construction, or at least the SR's. I also now have multiple options on how to approach threading the front block area of stacked tube bodies. Very much appreciate your sharing of the entire process of single point threads cut shallow and finished with a tap. Legit take away knowledge that I very well would have neanderthal bungled otherwise.
If I don't answer, please leave a message.
I will call you back.
|12-12-2018, 05:03 AM||#7 (permalink)|
King of Low-End
Join Date: Aug 2011
Location: St. Louis Missouri
A few minor corrections to the SR’s history. It wasn’t made in China, but Taiwan (FWIW), same place the relatively well made Trilogy’s had been made for 4 years at that point. And that I’ve never seen a single SR’s electronics die. Only the boards OLED’s had a reputation for failing, not the boards themselves. There’s even a guide on how to completely program the SR blind out there somewhere I recall.
|12-12-2018, 01:15 PM||#8 (permalink)|
Join Date: Mar 2008
First Strike Paintball
|12-12-2018, 01:28 PM||#9 (permalink)|
Join Date: May 2012
[QUOTE=kevin qmto;3541826. Only the boards OLEDís had a reputation for failing, not the boards themselves. .[/QUOTE]
Ok sure, but that's like saying "my car is not broken, just none of the door handles work"
The user interface is still broken. If you are ok climbing in through the window then yes, you can still use it but it's not like everything is 100% in working order either.
Technically you could program any marker blind if you know where you are in the settings, it's just the Sr is one of the only markers that it happened to often enough for anyone to put effort into writing a guide for it. Call it what you want but I would not call the electronics good if players are having to find their own way to program them because the way you intended them to do it does not work any longer
^^^ If you are new to the sport and need help finding gear, click here!!!^^^
|12-12-2018, 03:33 PM||#10 (permalink)|
Join Date: Jan 2015
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