I did not like the safety valve design in the text book. Text book valve can be adjusted for the blow starting pressure, but not for blow stopping pressure. The valve spindle is quite long and protrudes from the safety valve adjusting nut. I wonder the purpose of this is to stop the blowing by hitting the head of the spindle. Actually I saw a club member hit the spindle to stop the valve blowing in a club steam up.
So I decided to use Kozo Hiraoka's design that much more complicated than text book one.
I had no confidence to make a valve seat properly deep in the safety valve body and made the valve seat as separate part.

I heard the roundness accuracy of valve ball was quite important to have good sealing and found mail ordered high accuracy stainless steal balls.

 

At first I turned lock nut for adjusting plug from 10mm AF brass hex rod with M7 fine thread.

まずは一番簡単な調整プラグのロックナットから製作。M7細目のタップを立てた10mm六角真鍮棒を削るだけ。

Parted off side was cleaned out fixed on a mandrel.

突っ切った側はヤトイに取り付けてきれいにします。

aSafety valve body was processed:

4.9 drill -> 6.3 drill -> M7 fine tap

After these the bottom of the 6.3 drill was made right angle with a D-bit.

安全弁本体は4.9mmドリル、6.3mmドリル、M7細目タップを立てた後6.3mmの段差部分をほぼ直角とするため6.3mmのDバイトでさらいます。

After drilling outer shape was turned using parting off bit only. Turning brass was easy enough only by parting off bit.

その後、外形を切削。バイトを換えるのが面倒だったので突っ切りバイトだけで削ってしまった。相手が真鍮なので突っ切っりでも楽なもんです。

At this stage I measured the depth of 6.3mm hole. This depth seemed important in Hiraoka style safety valves.

ここで6.3mm穴の深さを正確に測っておきます。ここいらの寸法は平岡式安全弁では重要なようです。

The valve body was turned over and reamed with 5mm reamer to accept separate valve seat.

弁本体をひっくり返し、バルブシートが入る穴に5mmのリーマーを通し、

The out side was threaded with M8 fine.

外にはM8細目のダイスを切ります。

Total length of the valve body was measured to decide the valve seat dimensions.

ここで、安全弁本体の全長を測定。これと前に測った6.3mm穴の深さを元にバルブシートの寸法を決めます。

Valve seat surface was turned with angle of 15 degrees.

バルブシートはシート面に15°の傾斜をつけるため、こんな設定で削りました。

Valve sheet surface with 15 degree angle.

15°だとこのくらいの傘型になります。

According to Kozo's book the valve seat need to be made by hitting a ball to the valve seat. Again I did not confident on this job. So I used “burnishing” method to finish valve sheet. So I made a burnishing tool as this.

バルブシートはボールを打撃する方法は難しそうなので回転しているバルブシートにボールを押し付けるバーニッシングという方法で行うこととしこんな道具を作りました。

Failure

I put the tool above to the tailstock and pushed to the valve seat turning at 1000rpm. However it was a total failure, because it was almost impossible to control the pushing pressure by tailstock screw. The pressure was too strong and the seat surface was too wide. The ball of the tool was stuck with brass and damaged.

失敗

上記道具を芯押し台につけてバルブシートを1000rpmで回転させて押し付けてみた。これは完全な失敗であるな。心押台を使うと軽く押し付けることができず、シート面が幅広くなりすぎてしまった。さらにSUS球には真鍮がこびりつき傷も入っている。