Author Topic: Bottled Disco Frankengun (Help!) (Read 13191 times))

Gerard · « **Reply #40 on:** August 24, 2016, 12:50:16 PM »

Exactly Jason. I found my previous seal, the one which came with my already-modded QB78D, was gradually getting more distorted through all the disassembly/reassembly cycles as I worked on various tuning elements. After probably 50 cycles it wasn't sealing very nicely, blowing a bit of tissue paper noticeably. It was made of something slightly harder than PTFE, probably a softer sort of nylon though I'm not certain. It wasn't a huge amount of air leaking but any air is more leak than I want.

Hm, how to compare Teflon and urethane... Teflon is like carving a firm, evenly moist Parmesan cheese. Only easier, as it slices incredibly smoothly. Polyurethane is more like carving a superball. In fact I'd bet many superballs are probably urethane, perhaps all. On a scale from 1 to 10 with 1 being extremely easy and predictable and 10 being so frustrating as to make one abandon a material for something less confidence-destroying, I'd put Teflon around 2 and 95 durometer polyurethane around 8. In a 1" rod (the size I picked up from an eBay seller some years ago when I was hoping to make a piston seal for my Baikal 46m - couldn't do it by the way, much too difficult for me, though I may try again some day now I have more practice) it is almost wood-like in stiffness and apparent hardness, sort of like pine. In the dimensions of a transfer port it is squishy, easy to distort, making it necessary for the tools to be extremely sharp and the lathe spin to be fairly high. Cuts extremely easily, no resistance, but tends to grab the tool. I'm not recommending it for its ease of use. I just love how it works when I finally get one made in the perfect dimensions. It'll survive any number of rebuilds.

David Mccann · « **Reply #41 on:** August 24, 2016, 01:16:31 PM »

do you have a link to the mini lathe you bought??

aPpYe · « **Reply #42 on:** August 24, 2016, 01:27:11 PM »

Googling "elastomer" ... (doe-eyed newbie staring at the headlights) ...

Okay, so teflon would be an example of a rigid material, and polyurethane is an elastomer then? Since it is the only plastic rod of any kind (besides hot glue sticks) that I have in my posession, I will go ahead and use that for now. If I find that I keep taking the thing apart, I may look into an elastomer.

On another note, it seems I will be turning down the nose end of the probe, being careful not to get too close to the oring slot. My understanding is that anything protruding over the barrel port is a restriction:

My understanding is that the little lathe I bought should do okay turning brass or aluminum, so I may try my own take on a retracting bolt. I wonder how well Bob's "j-slot" retractable bolt seals compared to a traditional o-ring design. I was thinking of something more along the lines of having a retractable probe inside of the bolt. Of course, there's the whole "bolt handle threads are in the way" issue ...

I should be doing the machining and (hopefully) assembly on Friday, assuming everything arrives by then, and I don't chicken out. That's the big thing for me, I only have one chance to get this right!

David, here is the link:
http://www.ebay.com/itm/181991146540?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Gerard · « **Reply #43 on:** August 24, 2016, 02:00:19 PM »

That looks like a nifty little machine. My only concern when reading through the description is that it keeps mentioning a motor speed of 20,000rpm, with no mention of gearing that down to different speeds. The 300rpm to 1,200rpm range is practical for metal machining, but 20,000rpm could be dangerous to the user as well as being extremely difficult to work with. Let us know how it works out.

nervoustrigger · « **Reply #44 on:** August 24, 2016, 02:10:23 PM »

Right. Teflon is a rigid material with very little elasticity. When forced into a particular shape, it pretty much stays that way.

Contrast that with an elastomer (elastic polymer). What the layperson would generically refer to as rubber.

Regarding the bolt probe, yes it would benefit from backing the tapered section up where it obstructs the port.

Quote from: aPpYe on August 24, 2016, 01:27:11 PM

I wonder how well Bob's "j-slot" retractable bolt seals compared to a traditional o-ring design.

Hmm, well usually a retractable bolt seals in the same manner with an O-ring on its shank. Just give some thought as to how far forward the O-ring must go to seat the pellet, and where it will come to rest when withdrawn to clear the barrel port. That path needs to have parallel walls so it may be necessary to shape the chamber to accommodate the O-ring coming forward farther than usual.

aPpYe · « **Reply #45 on:** August 24, 2016, 03:31:32 PM »

Well, the whole idea of a chamber without a probe is gonna have to wait a bit anyway, depending on what I am able to glean from this gun. So far, the 10.3gr and 13.4gr slide right into the chamber without any marks from my .025" probe. The 16.2gr pellets are a tighter fit and do exhibit a light dent where it comes in contact with the probe. I will not know how that affects things until after I fire the gun of course.

Quote from: Gerard on August 24, 2016, 02:00:19 PM

That looks like a nifty little machine. My only concern when reading through the description is that it keeps mentioning a motor speed of 20,000rpm, with no mention of gearing that down to different speeds.

I believe it was just referring to motor speed, and not shaft speed. Likely it is only one speed though. I might be able to fashion a regulator or something to slow things down. It is obviously not the most accurate machine in the world, but for a newbie, I think it is perfect for now. If I really get into this, I may pick up a real lathe and/or mill.

David Mccann · « **Reply #46 on:** August 24, 2016, 04:00:08 PM »

looks like a cool little gizmo. versatile too. probably works just fine for small light duty stuff.... cheers

aPpYe · « **Reply #47 on:** August 24, 2016, 08:04:33 PM »

sigh. This is disheartening. When they came in the mail a couple of weeks ago, I turned the "GAUGE ADAPTER FOR BENJAMIN MARAUDER AIR RIFLES" (as it is listed on "archery's" website) into the PRod Gauge port about 4-5 turns. It seems like it went in okay, and I have not yet inspected the threads on the gauge adapter, but now I am seeing a post in another thread by Bob saying that they are not compatible, as the adapter is straight thread and the port is npt... I hope I did not screw up gauge port. What is bothering me is that it says right on their website that it "Also fits Benjamin Discovery air rifles and Benjamin Marauder pistols, Model BP2220." ... even though on closer inspection, the adapter is nowhere to be found on the PRod EVP...

First, they sent me an MRod port instead of a PRod port, and insisted that I pay for shipping back to them (rudely, I might add ... The lady on the phone kept cutting me off and tried to tell me that this is the way it always works when ordering things from anywhere on the internet) before they would "reimburse" me (shipping was about $4.50 and their "reimbursment" was barely $2.00) for the shipping and send the correct part back, now I find they are mislabeling things on their website. I am not sure how I feel about this ...

Do you guys think I messed up the threads on my gauge port? I do remember that the threads do seem to interlock pretty well when putting two male ends against each other, so I figured everything was good ...

aPpYe · « **Reply #48 on:** August 29, 2016, 04:10:46 PM »

Okay, so I am learning. Without a return spring, I was able to fill the gun up without any problems. Perhaps this is because I first "feed" the pump with 130psi from my shop compressor to get the first 1000 pounds into the gun, then I drop the shop compressor's regulator pressure down to about 30-50psi and fill the gun the rest of the way from there.

Anyway, I did my machining (more on this later) and got the gun together. The bottle mounts on there SOLIDLY through the gauge port and with the plastic mounting brackets I had on there. Awesome.

Of course, this wasn't going to go without any problems... I seams I had a LEAK! I am pretty sure it was at the seat...
With 1500psi in the tube, and with the bolt closed and hard against the breech, I can put my finger over the end of the barrel and feel pressure build up against my finger. When I release my finger, I get an audible release of pressure there. Either I did not adequately clean the dust opening the exhaust port, and some bits got in there ... Maybe it was when I was using hex keys to get a throat diameter, I nicked the seat somehow! I dunno. At first, I thought the poppet needed to be broken in (the new poppet lacks the groove that was worn into the original poppet by slamming into the valve seat thousands of times), so I dry fired the gun to empty. Refilling it did not avail any improvement. To make a long story short, I tried and failed (horribly!) at resurfacing the seat and the valve is probably ruined ...

On to my question: I still have the original CO2 valve that came with my 2400kt. If I can manage to get the holes centered correctly for the other two valve pins, is it safe to use the back half of this valve? Other than only having one pin hole, it seems identical at first glance, other than it being brass and not aluminum. Is it bad to have a brass back half and an aluminum front half? If not, then I am gonna have to wait another week for a new valve ... sigh.

aPpYe · « **Reply #49 on:** August 29, 2016, 07:24:40 PM »

Hmm... It should probably be noted that I did try to streamline the poppet by turning it into a slightly more aerodynamic shape:

...Perhaps the leak is going THROUGH the poppet somehow?

I made sure that I did not change the diameter of the edge where it contacts the seat ... and the face (sealing surface?) of the poppet seems undamaged and feels smooth all the way around:

Unless anyone dissuades me, tonight, I will try my hand at converting the rear side of brass CO2 valve to this gun. As I understand things, I need to get the screw holes centered just right as well as file flats on the hull to allow the screws to fully seat. Then I will have to put another piece of that hobby tubing in there to get the stem sitting pretty.

aPpYe · « **Reply #50 on:** September 08, 2016, 01:34:23 AM »

Okay, so this will be valve number THREE I have screwed up. The first was the original disco valve (rear half) I had that would not seal at the poppet. The second was the rear half of the brass 2400kt valve that I tried tapping. The tap went right through into the valve throat. This one, while I was enlarging the port, I wasn't paying close enough attention, and drilled right into the adjacent valve pin hole.

... Being in the throat, and not in the main part of the valve, would it still seal if I were to goop the screw with lots of threadlocker? Maybe ptfe tape? How badly would it affect efficiency and/or performance, seeing as how that section of the throat would no longer be perfectly round? I would think (maybe the operative word is "HOPE") that with the screw filling in the hole just about all the way to the throat, it would be negligible. Most importantly, would it be safe to use? It would only be holding back pressure during a shot, as it is not in the HPA side...

These setbacks have been a learning experience to say the least ......

nervoustrigger · « **Reply #51 on:** September 08, 2016, 01:45:45 AM »

Yeah, it's not ideal but it's more of a psychological setback than an actual one.

A number of folks have drilled into a valve throat while adding anchor points to secure the valve. Your are correct that some threadlocker on the screw will seal it, but even lacking it, there would not be enough loss through the threads during the very brief time the valve is open for it to really matter.

aPpYe · « **Reply #52 on:** September 08, 2016, 02:52:23 AM »

Well, I feel better now then!

It seems I just might be finally putting this gun back together after these weeks. I will be sure to share every hair pulling detail and post pictures of this ~~hackjob~~ learning experience.

aPpYe · « **Reply #53 on:** September 10, 2016, 05:35:56 AM »

I am finally seeing a light at the end of this tunnel! All I have left to do is the transfer port, and I have plenty of material to go through in case I mess up. I wanted to check with you guys on something though:

Now that's COMEDY! Is it still gonna work, or will the stem end up coming loose now? Is the poppet just molded around a straight piece of stem, or is it molded around something bigger as well? I made sure I had a spare before I started hacking away at this one...

Gerard · « **Reply #54 on:** September 10, 2016, 09:00:19 AM »

If that's a delrin poppet, then yeah, no, that's gonna come loose as it's just press-fit onto the stem. Black comedy indeed! Ouch! By the way, a bit of 0000 steel wool polishes delrin nicely if you don't spin it too fast and melt the stuff. Just go easy, pause to let it cool, and you can get quite a decent finish, although of course a lathe and sharp tooling work better.

aPpYe · « **Reply #55 on:** September 10, 2016, 12:11:11 PM »

well, i don't know what the material is honestly ... It is a stock m-rod poppet straight from Crosman. I am thinking that if it is just a straight shaft, then it will come loose, but if it is molded around something besides just a straight shaft ...

aPpYe · « **Reply #56 on:** September 10, 2016, 01:35:08 PM »

So this is what a Disco poppet looks like when removing the plastic part. I am wondering if the mrod stem is "over molded" around something similar. I suppose I could destroy my existing poppet and find out, seeing as how I do have a spare, but I was hoping someone could clue me in?

Matt15 · « **Reply #57 on:** September 10, 2016, 02:32:03 PM »

I took an Mrod stem apart before and it had groves in the stem that held the delrin on. I also did what you did to a stem before and it worked fine in my crosman 2100.

aPpYe · « **Reply #58 on:** September 15, 2016, 06:27:13 PM »

Okay, I ALMOST have this project finished. The turned down, cone shaped poppet has been holding so far, and the tube holds pressure over a couple of days without any movement of the needle.

Once I am ready to finally TUNE this thing, seek out the knee, etc, you will be seeing a MARATHON post I have been working on that chronicles the trials and tribulations I have gone through getting this hackjob up and running properly!

So last weekend I had a leak at the transfer port where I could feel a puff of air during every shot. I also had a leak at the breech seal, the o'ring that sits at the end of the bolt, sealing it to the chamber. Well, I got the transfer port sealed up really nicely and there is no air coming out of that during the shot.

The breech seal is still leaking however. What is odd, is that I never noticed this before. While I suppose it is possible that I just wasn't aware of it, seeing as how I was moving much less air, there are a few other things that are different now:

I installed a white polyurethane 90 durometer o'ring instead of the softer, stock black one.
I turned the nose of the bolt down so only the probe itself sits above the transfer port. The o'ring still seems to snap right into place though, and the part it is smashed against while the bolt is closed is unmodified... That is where the actual seal takes place I would assume.
I briefly spun the bolt itself in my drill press and lightly polished it with some 500 grit sandpaper.

My initial thinking is that this problem is two fold:

The 90 duro o'ring, being much harder than the original o'ring, does not seal against the barrel as readily.
Last winter, when I "polished" the leade and broke the sharp edge going into the rifling, I also worked the surface of the barrel that the o'ring sits against. The highest grit sandpaper I had at the time was 500 grit. I have since rectified this situation and I have 800, 1000, 1500, and 2000 grit sandpaper sitting next to me as I write this. I will be polishing it up tonight, and if this does not fix things, I will try it with the old o'ring...

I was thinking I may also try epoxy and some beer can material on the bolt handle, making it a little thicker, thus pushing the o'ring harder against the barrel when the bolt is closed.

Any other ideas?

aPpYe · « **Reply #59 on:** September 17, 2016, 05:08:37 PM »

Okay, so polishing things up did not help. Neither did the softer o'ring. The puff of air is definitely coming from the breech (bolt?) seal, and not the transfer port.

I am hoping someone can help me with this. I THINK I know what is happening. The o'ring may be extruding slightly into the elongated barrel port. At least this is what the current running theory is anyway...

What I am thinking now is that I can move up to a larger o'ring, and cut the channel on the bolt back slightly to move the new o'ring backwards from where the current one is. Any input is appreciated...

Here is what things look like through the barrel port with the bolt in the cocked position:

You are seeing a steel probe that is embedded in some nylon rod, which is inside of the brass bolt. The white o'ring looks sort of grey/green in the picture, and is what you see closest to the edge of the port. From straight up, I did not notice the o'ring before:

I did the ball grider thing on the inside part of the port as well, so whatever little bevel there isn't going to help the situation ...

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Bottled Disco Frankengun (Help!)

Author Topic: Bottled Disco Frankengun (Help!) (Read 13191 times))