Any one ever heard of the Dynamic PCP air rifle?

[Wolverineshooter]

Sounds the DAR needs improvement. I am glad l returned mine. Hopefully the next version will not have these problems

[nervoustrigger]

Back in business:


I used a piece of Delrin rod a GTA member graciously sent me a while back.  The steps were:

1.  Cut a piece 0.55" long.
2.  Center drilled it with a #32 drill bit to a depth of 0.325".
3.  Used a wood clamp to carefully press in the stem.
4.  Chucked it up in the drill press via the stem, and used a carbide burr in the Dremel to reduce the OD to 0.295" (same as the original poppet).  The Delrin rod was initially 0.5" diameter so I had about 3 cubic feet of little white shavings when I got done.
5.  Ground down the end for a seat for the valve spring.  Only made it about 0.1" tall...the factory one was 0.3" and there's no need for it to be that long.
6.  Made a lapping fixture by drilling a #31 hole in piece of scrap wood.  Used a hollow punch to knock a series of holes in a piece of 220 grit paper.

Note the hole was drilled with a drill press so it's nicely perpendicular to the wood's surface.  This aspect is not absolutely required.  If the hole is slightly angled, you can still successfully lap the poppet, it will just have a slight taper to it.
7.  Passed the poppet through the paper and through the wood, and grabbed the stem with a handheld drill and pulled against the sandpaper while spinning it.
8.  Used a black marker to color the sealing face of the poppet.  When the sandpaper has removed all the black, you know the surface is flat so it can seal properly.  It took a lot of cycles in this case.  I used all 20 holes you see punched in the sandpaper.  This sandpaper was old and worn though so it probably would have been quicker had I used a fresh piece.
9.  Lapped it a couple of final times for about 15 seconds each in the actual valve using J-B Bore Compound.

Once I had it all back together, it took just a few pump strokes before it sealed completely.

[Gertrude]

Nicely done Jason
Great write up.

[Wayne52]

Thanks for the great last reply you did there Jason, I've had this thread bookmarked since the day it showed up, if I need to make one it looks like the way to go.  I've got the perfect delrin rod that I originally bought for making HiPAC seals with, it's 3/8"(.375) which would cut down on the pile of shavings.

[mackeral5]

Jason---excellent write up on making poppets.  I will add that I actually find peek to be EASIER for me to "machine" and create perfect seals with than delrin.  I think I get in too big of a hurry and end up fuzzing and/or melting delrin.  Peek machines and even polishes almost like it was metal.  It handles heat much better so I can get away with using high speed to my advantage.  The hardest part is drilling a close to perfectly centered/square pilot hole to press the stem into.....but assuming the poppet is a little smaller than .375 a little off center/off square can be machined out.

After pressing the peek poppet on the stem, I chuck the stem in my dremel's flexible shaft----the flexible shaft's chuck has a wide range of adjustment so it will handle most poppet stem sizes.  I rely on high rpm and a light touch to "machine" perfectly round poppet bodies and perfectly square poppet seats.  The poppet seat/sealing surface is finished by running at max rpm, being careful not to get the part too hot. Step 1 is true the seat with a sharp file (the same file I use to reduce/shape the 3/8 peek rod with); step 2 is to smooth the seat with 500 grit wet/dry sandpaper; step 3 is to polish with 1200 grit wet/dry sandpaper.  Then color the seat with a sharpie, insert into the valve, and lightly burnish/lap with a cordless drill until a nice uniform circle is worn into the colored poppet face.

I hope that more members will read your post and realize most anyone with a dremel, cordless drill, and/or drill press can make replacement poppets.  it just takes some time.

BTW---I recently lucked out and scored a 3 foot section of 3/8 PEEK off of Amazon for $12.  Either it was clearance or a mistake on their end, but I snagged it the moment I saw it.  Can you say "poppets for life" lol.....

[Wayne52]

Mike I need to get some of that PEEK and try it some time, I've never used it.  Right now the delrin 3/8" rods I bought I had researched before buying them, they're very hard and tensile strength is over 7000psi. When I bought them it was for making seals for HiPAC's which I've run at 3000psi with no leaks.  I'm thinking that if I do have poppet problems with any of mine I might order some PEEK to try it out.

The seals on those HiPAC's I made replaced the original c02 sealing washer in the 22xx's.

[mackeral5]

Wayne, the delrin you have should work very well if you follow Jason's guide.  It is also more forgiving of valve seat imperfections.  I prefer peek in general primarily for the reasons I explained above.  But also, If you are making a poppet that seals against a tapered seat, peek is typically going to be a lot easier to knock open as it won't get wedged down in the seat like a softer material will.

[nervoustrigger]

Hi Ron, Wayne, Mike.  Thanks for the positive comments on the poppet.  I sincerely hope it will help someone who has a favored rifle out of commission.  It took a couple of hours to get it done but it was nice to be back up and running and I expect the Delrin piece will last a good long time.
 
Mike, thanks for sharing your experience with working PEEK.  I have a rod that I thought about using but since this rig is regulated at “only” 1500psi, I decided on the Delrin.  Based on comments from Bob and Scott (I think) that I ran across along the way, I kinda partitioned off PEEK in my mind as being mostly useful above 2000psi.  Not that it can’t be used at lower pressures but that the advantage in ease of opening is outweighed by the unforgiving nature of it sealing.
 
If you have experience using it at low-ish pressures, would you mind telling me what you think?
 
In exchange let me share something I wish I had done a long time ago.  Regarding the melting and fuzzing up problems with working Delrin with caveman tools, I’ve tried files and sanding discs and had some of the same issues.  A few months ago I picked up two small assortments of carbide burrs, one with 1/8” cutters and the other with 1/4” cutters (with shanks that fit a standard rotary tool…3mm or 1/8”, whatever it is).  I think each set of 10 was around $15 on Amazon.
 
They are amazing.
 
The first use was shaping a rear downslot in a steel QB receiver.  It’s something I’ve done several times before…drilling a starter hole as large as possible, cutting away what I can with a fiberglass or emery wheel, and then doing the final shaping with a round file.  The last part I dread, so much so that I’d procrastinate about doing it.  Let me tell you the first time I spun up one of the carbide burrs, I was skeptical.  Then the bit met the workpiece and little shavings started flying.  So easy to control, so effortless, great results…just beautiful.
 
And it turns out they work great on Delrin too.  Fast stock removal and doesn’t overheat the part, and leaves a surprisingly good finish that doesn’t take much time with a file to smooth out.

[mackeral5]

Jason---I agree those carbide cutters are awesome.  I have both ferrous (finer teeth) and non-ferrous (coarse teeth) versions, only in 1/8" shaft. 

While peek is less forgiving that delrin, so long as you have a good round valve seat with a consistently sized sealing surface you will have no problems with peek.  I've used it down to 90-100bar set points with no issues.  Ultra light hammers really compliment the peek poppet at lower pressures.

Note I've never run a hammer heavier than 20 grams with a peek poppet and lower pressures.  Heavier hammers may present a challenge due to the valve being so easy to open when running peek poppets at low pressure

Where it does present challenges is when your valve seat isn't close to perfect in shape and/or finish.  For example, when boring out a QB78 valve throat, if you have already hogged out and radiused the valve exhaust port the drill will try to walk up a bit (towards the valve exhaust port) when boring out the throat.  So you end up with a ever so slightly off center valve throat.  After lapping the seat one area of the seat is sometimes wider than the other.  This type of imperfection typically doesn't affect  soft oem poppets.  Delrin typically handles it as well.  Peek can be a little more challenging with imperfect valve seats. 

[nervoustrigger]

Mike, thanks for detailing out your experience with making PEEK poppets.  What you said about enlarging the throat on a QB valve makes sense, given the raised lip.  So far I think the largest I’ve drilled it out was just to remove the upward beveled portion which meant the flat was still (mostly) present to serve as the sealing surface.  I recall reading about your build...going for power so I assume you went with more aggressive porting. 

I think I’m going to start with the B50 that I’ll be (finally) starting on soon.  It will be a .25 cal conversion tuned for power at the full 3000psi pressure, so I’ll cut my teeth on that before trying it at lower pressure.

Meanwhile regarding the DAR, I’ve had some time with it since the repair.  When setting the hammer spring for the velocity knee, it ended up needing less by almost 3/4 turn.  That doesn’t sound like much but considering how coarse the threads are on the end cap, it’s huge.  Most of that difference  I assume is the Delrin being harder than the OEM material so I can appreciate the PEEK being another big step in that direction.

And it just makes me giddy when I sit down with a tin of the 34gr heavies.  Last night I went out in the cold and rezeroed it, stopping when two went through the aspirin-sized builseye at 43 yards. 

A couple hours later I took it back out again to send one pellet to the check for possible POI shift (reg creep).  When I saw the glint from the flashlight reflect off the skirt as it passed through the same hole as the previous two pellets, I was in disbelief.

If they can get the QC sorted out on these things, they’re going to have a winner.

[Gertrude]

 .... And it just makes me giddy when I sit down with a tin of the 34gr heavies.  Last night I went out in the cold and rezeroed it, stopping when two went through the aspirin-sized builseye at 43 yards. 

A couple hours later I took it back out again to send one pellet to the check for possible POI shift (reg creep).  When I saw the glint from the flashlight reflect off the skirt as it passed through the same hole as the previous two pellets, I was in disbelief.

If they can get the QC sorted out on these things, they’re going to have a winner.

I have been consulting with DAR on a regular basis.
 I'm waiting to hear from them that the parts and changes we have discussed are here.
Once that happens, trust me, I will be working on it to get these rifles up to their full potential.

[Wayne52]

These work really nice in the DAR25

very easy getting over 60fpe with it too.

[nervoustrigger]

Thanks Ron, I’m glad to hear that.  It can only benefit their designs to have you consulting with them, and in turn that makes them better for everyone.

Wayne, I really wish you would quit reminding me that you have yours churning out 60fpe!

I’m afraid to fool with mine.  It’s one of the most accurate air rifles I’ve ever used so I’m going to keep riding it out at a more modest power until I can’t find JSB Heavies it likes. 

[Wayne52]

Jason I've since turned mine down to around 50fpe shooting the 26 grainers, I get a lot more shots this way with fantastic accuracy as well.

[KnifeMaker]

For those that don't want to spend the money for peek. (Mike is a lucky man, I just paid 20 bucks for 6 inch rod of peek). Grrrrr!!!


There is a product called PEP-T that is pretty much between delrin and Peek, and dirt cheap!


It does very well at 3100 psi. RKR is using it in his mega FPE builds.


but then again, It isn't Peek. Which is 40% stronger than Delrin according to a manufacturer spec sheet that makes both. It also handled higher heat!


Knife.

[nervoustrigger]

It's PET-P for those interested in researching it.  Also sold under the trade name Ertalyte.

In a quick search, Grainger's pricing stomps a mudhole in Amazon's but I imagine shipping levels it out.

https://www.grainger.com/category/raw-materials/plastics/plastic-rod-stock?attrs=Material%7CPET-P&filters=attrs

[KnifeMaker]

The PET-p I ordered was priced the best at McMaster car for me. I didn't think to check wit granter. The PEEK I ordered on Ebay. Kinda high but no shipping charge so it worked out.


Knife

[Wolverineshooter]

Any news when the updated DARs will ship?

[Gertrude]

Any news when the updated DARs will ship?

https://www.gatewaytoairguns.org/GTA/index.php?topic=150686.50

[Wolverineshooter]

Any news when the updated DARs will ship?

https://www.gatewaytoairguns.org/GTA/index.php?topic=150686.50

Thanks Ron. No hurry, hope they get a good one this time.