TX 200 Breech seal

[Vernal]

Once again, excellent info for the 'very useful to know file'.
I had begun to search for TP info and found reference to the TX200 MK3 having a port of around 3.7 - 3.8 with the MK1 and 2 having the narrower port of 3.2.


Cheers, Phil

I measured mine using drill bits- 3.6 fitted, 3.7 just didn't, so it could well really be 3.7.
It is a Mk.3 tube running a Mk 2 piston - would it be worth looking for a Mk 2 tube?

[Vernal]

I can't think what prompted me to do it, but I just took a look at the inside of the transfer port using a 10X lens. Shock horror, at first I thought someone must have started to cut an internal thread in it, but a closer look shows that the row of grooves about 0.1 - 0.2 mm deep are not helical, but in series going most of the way down the port (I wish I could photograph this). Another check found that the 3.7 drill, which will not fit into the entry end (see my earlier post) goes about half way through from the exit end.
I know that a polished surface is not considered a must for the tp, but the turbulence as the air passes over these deep grooves must be immense, so much so that it may be the cause of the gun struggling to make full power?
So what should I do now? I don't have the engineering facilities to sleeve the port and as far as I can see the end plug is not available separately as a spare. Should I try opening the port to 3.8, which should get rid of most of the rings, or do I give up and buy a whole new cylinder? I don't like the idea of just leaving it as it is

[Turnup]

Interesting observation. You observe a slightly tapered TP with circumferential ribbing and that seems unlikely to be accidental to me.

Might be a red herring but I am minded of a certain German aircraft (Junkers sommat or other?) which has a ribbed surface on the fuselage perpendicular to the air flow. Was originally done to increase stiffness but they found, contrary to instinct, it actually reduced parasitic drag by disrupring the laminar air flow. This is a low speed aeroplane and different effects might prevail as the air velocity increases. Also air flows in the confined space of the TP could be entirely different. Are they all like that I wonder?

[Vernal]

Interesting observation. You observe a slightly tapered TP with circumferential ribbing and that seems unlikely to be accidental to me.

Might be a red herring but I am minded of a certain German aircraft (Junkers sommat or other?) which has a ribbed surface on the fuselage perpendicular to the air flow. Was originally done to increase stiffness but they found, contrary to instinct, it actually reduced parasitic drag by disrupring the laminar air flow. This is a low speed aeroplane and different effects might prevail as the air velocity increases. Also air flows in the confined space of the TP could be entirely different. Are they all like that I wonder?

The grooves do not look nearly regular enough to be intentional, they vary significantly in width, depth and separation, and look as if a piece of damaged tooling was used to make the hole - probably whatever Air Arms used to make it in the first place. Can't imagine how it could have got through QC though.

[Shed tuner]

either leave the port alone, or sleave it down to 3.3
cleaing it out will just increase the flow, and it's already a bit too big.

[TonyL]

Michael, I'm guessing that the end plug is still not re-attached to the tube? At the risk of sounding a little casual (as I've not yet sleeved a port myself), surely now would be the ideal time to find a way to get it done? I think it would play on your mind afterwards if you didn't do so.

I know Jon's used radio aerial material to do them in the past. With the end plug now removed I wonder if you could relieve a little from the inside face allowing a "mini top hat" arrangement loctited in as the new TP with your chosen diameter?

[Vernal]

Michael, I'm guessing that the end plug is still not re-attached to the tube? At the risk of sounding a little casual (as I've not yet sleeved a port myself), surely now would be the ideal time to find a way to get it done? I think it would play on your mind afterwards if you didn't do so.

I know Jon's used radio aerial material to do them in the past. With the end plug now removed I wonder if you could relieve a little from the inside face allowing a "mini top hat" arrangement loctited in as the new TP with your chosen diameter?

It certainly would prey on my mind if I didn't do something Tony, and I have thought a lot about an amateur sleeving job. I have brass rod to use as the insert and I can drill a fairly decent concentric hole using an engineering chuck in my Myford woodworking lathe, but it is the entry end of the tp that bothers me. This has quite a deep chamfer on the inside of the end plug which seems to go on into the tp. It almost, but not absolutely convincingly, looks as if the current tp is an insert. I might end up having a go at it, but it might be easier to find a new end plug if such things exist.

[TonyL]

Jon, Mick or NickG would be the best people to advise, Michael. Now, Jon and Mick don't take jobs on for others. But I think Nick would? I wonder if it would be worth dropping him a pm? You might be able to post the end to him and he post back to you. And he has played with (and modded / made) plenty of comp tubes.

[Shed tuner]

the current (factory) TP is indeed an insert....

just glue in some brass tube, push it from the inside... thin tube will naturally flare a little and get lodged in the taper... If you are making from solid, by all means leave a little lip. if the end plug is off, very easy to tidy up afterwadds and add a minute champfer.

[Vernal]

Jon, Mick or NickG would be the best people to advise, Michael. Now, Jon and Mick don't take jobs on for others. But I think Nick would? I wonder if it would be worth dropping him a pm? You might be able to post the end to him and he post back to you. And he has played with (and modded / made) plenty of comp tubes.

Nick G has done some super work for me in the past, and is certainly someone to try if I outsource the work, but my cussed self reliance and sheer over-ambition means that I shall probably have a go myself before I ask someone else to rescue my failure.

[Vernal]

the current (factory) TP is indeed an insert....

just glue in some brass tube, push it from the inside... thin tube will naturally flare a little and get lodged in the taper... If you are making from solid, by all means leave a little lip. if the end plug is off, very easy to tidy up afterwadds and add a minute champfer.

Thanks Jon, but I am not sure that I have any tube thin enough. What size finished tp should I be aiming for please?
My initial thought was to drill and tap the end plug to take an M8 threaded insert, then to make a new insert from apiece of 8mm mild steel rod, threaded with the die only closed enough to let the insert fit tightly into the end plug and the protruding stud reduced to 7mm dia as the existing one. Insert from the inside to get the projection right, then cut off the excess and file flush with the plug. Does this sound sensible, or am I un-necessarily complicating things?

[Phil Russell]

Out of interest I tried to find some thin walled steel tubing and failed to find any thinner than c 0.5mm and then the id was not perfect. I noted the use of radio aerial tubing and find that such telescopic aerials are available cheaply on the 'site' but do not have sizes of the tubes in the description. I am not about to sleeve a TX compression cylinder but if I was I would consider drilling the current TP out to take a brass or steel insert, maybe 4mm or so od with a new TP drilled through the insert at whatever is needed. My spare compression tube, which is a MK3, has a 3.6mm TP with smooth sides. I have the matching piston which has the latch rod extending 31mm beyond the skirt. The MK2 measures 45mm I believe.

But: if 3.6mm is the standard MK3 TP is there a benefit to sleeving it down even if everything else is standard? i.e. not short stroked or whatever.

Cheers, Phil

[Shed tuner]

But: if 3.6mm is the standard MK3 TP is there a benefit to sleeving it down even if everything else is standard? i.e. not short stroked or whatever.

Cheers, Phil

I thouth it was short stroked to MK2 specs

[Shed tuner]

Thanks Jon, but I am not sure that I have any tube thin enough. What size finished tp should I be aiming for please?
My initial thought was to drill and tap the end plug to take an M8 threaded insert, then to make a new insert from apiece of 8mm mild steel rod, threaded with the die only closed enough to let the insert fit tightly into the end plug and the protruding stud reduced to 7mm dia as the existing one. Insert from the inside to get the projection right, then cut off the excess and file flush with the plug. Does this sound sensible, or am I un-necessarily complicating things?

I've done exactly that before, I think Nick has too, but it's too much work. Just get some brass or steel antenna tubing and find a bit that fits.

at mk1/2 stroke lengths, 3.2-3.5 is optimal, depending on lots of factors. If your piston is factory weight, smaller port (3.2) If lightened to around 190g, 3.5 is good. Ish.

[Phil Russell]

I thouth it was short stroked to MK2 specs

I think there is confusion here (apologies) ... the piston and comp tube I am talking about is mine, a bog standard Mk3 ... 3.6mm TP and standard length piston from a MK3. Not a MK3 comp tube running a MK2 piston.

The system Vernal is talking about is a MK2 one mated to a Mk3 compression tube..... so I do understand that a reduction in TP diameter could be useful.

My question was 'is it worth reducing the TP on a bog standard MK3 to c. 3.2mm as used on a MK2'.
Cheers, Phil