D bits

[Boiler BriParticipant @boilerbri]

I have never made a D bit so I thought it was about time I had a go. I ended up using a 1/4" hss drill bit. After cutting all the fluting off I gently ground the bit until it measured up to what I needed. Square on the end and exactly half the diameter. The half diameter being flat to the axis of the shank.

So should I counter bore the hole to just short of the finished hole depth and say 3/16" diameter or should I just go straight in with the D bit?

I can't try it or practice because my lathe has the valve set up in it ready for me to do the deed.

Your advice please.

Brian

[Boiler BriParticipant @boilerbri]

[Neil WyattModerator @neilwyatt]

For best results treat it like a reamer, leave it 1/32 or 1/64 to remove.

[Boiler BriParticipant @boilerbri]

Right. Thanks Niel. I did not want to jump in and have a go then mess my valve up.

Brian

[Maurice Cox 1Participant @mauricecox1]

The advice always used to be that the D of the D bit should be a couple of thou greater than half the diameter so that it cannot cut on the side and produce an oversize hole.

[Boiler BriParticipant @boilerbri]

Ok Maurice. I will let you know how I get on.

Bri

[Anonymous]

Assuming a flat bottomed hole is required the non-cutting half at the end of the D-bit should be relieved, otherwise one side will cut and the other side will rub. If one is not worried about exactly flat bottomed the whole end of the D-bit can have a slight chamfer.

The hole should be predrilled undersize, but generally no need to bore. If the D-bit is properly relieved it acts as a fairly stiff boring tool.

Errr if the D-bit is made from the shank of a drill the shanks aren't normally hardened.

Andrew

Edited By Andrew Johnston on 26/08/2018 19:17:50

[Boiler BriParticipant @boilerbri]

Hi Andrew, its only cutting PB1 so it should be ok. I think the relief might be a good idea.

Cheers

[Simon CollierParticipant @simoncollier74340]

It is not always possible but I prefer to make screw in seats I can face in the lathe. The finish left by my D bits is never satisfying.

[jason udallParticipant @jasonudall57142]

I know it’s obvious but check your drill shank is the desired size ….

[HopperParticipant @hopper]

And don't grind the shank down too far beyond the flutes. Most/many drill bits have a soft shank welded to the HSS fluted section.

[Boiler BriParticipant @boilerbri]

I chose a quality bit to try it with and cut the flutes to leave solid metal.

I never though of using a threaded removable seat. I might have a bash at that later.

There for a 5" engine back head, the hand pump on one and the axle pump on the other. The two injectors go in above the water level. I will re make the two later ones when I have the back head ones done and I am happy with them.

Brian

[Boiler BriParticipant @boilerbri]

Ok here's the results of my efforts.

 

PB1 material. I still have to clean up the edges and round the back off to suit the existing ones.

The seat has not had the ball seated yet as i have to make a guide for the punch.

A fellow forum member very kindly sent me some drawings of his valves with O rings fitted. I have drawn these up and if i am not happy with the ball method i will be converting them to O ring.

6MM D Bit

I still have some parts to make before i can test them, new top cap etc.

 

Brian

Edited By Boiler Bri on 30/08/2018 20:44:35

[michael howarth 1Participant @michaelhowarth1]

That O ring check valve looks interesting. Is the O ring mounted on a spring loaded plunger?

Mick

[Boiler BriParticipant @boilerbri]

 

 

Hi. The o ring is mounted on a small spigot to stop it wandering the spigot is just over halfway through the o ring and to the same shape. It needs about .2mm to squash down

 

 

Hope that helps.

Edited By Boiler Bri on 31/08/2018 20:10:08

[michael howarth 1Participant @michaelhowarth1]

Thanks Brian. I shall try one out on a vertical boiler I am building.

Mick

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