D bits

This topic has 15 replies, 8 voices, and was last updated 31 August 2018 at 20:36 by michael howarth 1.

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26 August 2018 at 17:01 #369151
Boiler Bri
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@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
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26 August 2018 at 17:01 #26158
Boiler Bri
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@boilerbri
26 August 2018 at 17:15 #369152
Neil Wyatt
Moderator
@neilwyatt
For best results treat it like a reamer, leave it 1/32 or 1/64 to remove.
26 August 2018 at 18:03 #369167
Boiler Bri
Participant
@boilerbri
Right. Thanks Niel. I did not want to jump in and have a go then mess my valve up.

Brian
26 August 2018 at 18:07 #369168
Maurice Cox 1
Participant
@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.
26 August 2018 at 18:17 #369169
Boiler Bri
Participant
@boilerbri
Ok Maurice. I will let you know how I get on.

Bri
26 August 2018 at 19:17 #369179
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
26 August 2018 at 20:41 #369193
Boiler Bri
Participant
@boilerbri
Hi Andrew, its only cutting PB1 so it should be ok. I think the relief might be a good idea.

Cheers
26 August 2018 at 22:03 #369203
Simon Collier
Participant
@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.
26 August 2018 at 22:05 #369204
jason udall
Participant
@jasonudall57142
I know it’s obvious but check your drill shank is the desired size ….
27 August 2018 at 02:26 #369220
Hopper
Participant
@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.
27 August 2018 at 08:35 #369232
Boiler Bri
Participant
@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
30 August 2018 at 20:42 #369725
Boiler Bri
Participant
@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
31 August 2018 at 06:09 #369758
michael howarth 1
Participant
@michaelhowarth1
That O ring check valve looks interesting. Is the O ring mounted on a spring loaded plunger?

Mick
31 August 2018 at 20:06 #369858
Boiler Bri
Participant
@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
31 August 2018 at 20:36 #369864
michael howarth 1
Participant
@michaelhowarth1
Thanks Brian. I shall try one out on a vertical boiler I am building.

Mick
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