D bits

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

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

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

Brian

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.

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

Bri

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

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

Cheers

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.

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.

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

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

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

Mick

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

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

Mick