Valve seat cutters.

[gabby]

Hi there all, A question about Valve seat cutters, is there a thread or information on making said tools to suit our modelling of the I.C. Valve seat and guide assy. 'coz I seem to remember somebody making a cutter using the valve guide to keep the seat true and square to the guide.
Also, 44degree valve into a 45degree seat, how does that work and is there advantages in making them like that.
Cheers
Gabby
:hDe:

 

[enfieldbullet]

i've never heard of the different angles thing. but i must assume that you could fabricate them like that to ensure that the valve will seat all the way in the valveseat. you should however need to grind/lap them together to ensure near perfect mating of the surfaces.

 

[MuellerNick]

Also, 44degree valve into a 45degree seat, how does that work and is there advantages in making them like that.

Yes, that has been done to speed up the initial lapping in of valves.
Using the valve guide (with a pilot pin on the cutter) is what all commercial tools do. BUT with the small diameters in model engines, that setup gets quite wobbly. It doesn't scale down linear. Half the diameter is 8 times less rigid.
So the best you can do is to machine the guide and the seat in one setup (be it mill or lathe).


Nick

 

[deverett]

The thinking behind the different angles between seat and valve goes like this:

If both parts are the same angle, there is more area to get a proper seal, but if there is only line contact using the different angles, it is easier to get a perfect seal. Minimal lapping is required with this method. Too much and you are back to the original situation.

Dave
The Emerald Isle

 

[Brian Rupnow]

There is info about one on my Kerzel build and on my Atkinson build.---May be some info on my odds and Ends build.---Brian

 

[gbritnell]

Hi Gabby,
I'm sure I had posted this before but rather than looking it up I will repost it.
gbritnell

View attachment VALVE SEAT CUTTER INSTRUCTIONS.pdf

 

[MachineTom]

In automotive engines the materials used for valves, especially exhaust valves are high temperature tolerant. Most model engine builders use drill rod or the like. When you give the valve to seat an interference fit, which automotive tends to 44.5° to 45° the line contact is poor to transfer the heat of the valves into the head. Remember that exhaust valve head hits the gas stream and instantly becomes red hot as the gases flow past, then the red hot valve hits the seat and begins to cool off. I'd suggest matching valve and seat angles in model engines, with a light lap and be done with it.

Few of the model engines built are ever run under heavy load, although model aircraft engine do sometimes fly. So it may be overstating the concern of burned valve, pre-ignition issues. A hit and miss engine loaveing along at with no load is unlikely to see an issue at all.

 

[123RWO]

I cut my last set of valve seats with this tool. http://www.brownells.com/gunsmith-t...ing-cutters/45-chamfer-cutters-prod41716.aspx It has a pilot hole with a set screw for retention. You make your own pilots to whatever size you need.

RWO

 

[ShedBoy]

I have only ever done 2 valve seats and just done it in the lathe after boring the valve pocket and guide hole just put the top slide on the 45° and cut the seat to about 0.25mm wide. I left the top slide on the same setting to make the valves. Minimal lapping needed and sealed good. 3 angle valve seats would be unnecessary in a model engine is my opinion.

Brock

 

[gabby]

Hi there all, hey many thanx for all the replies and the very useful leads.
Hi Gabby,
I'm sure I had posted this before but rather than looking it up I will repost it.
gbritnell

VALVE SEAT CUTTER INSTRUCTIONS.pdf (23.1 KB, 84 views)
__________________
Talent unshared is talent wasted.

This is the cutter I was trying to find, So now I can go forth and modify a little, I think I would like to add a drill bit in the sharp end to cut the Valve guide hole as well then everything would be alined.
Has this been tried?
Cheers
Gabby ;D

 

[gbritnell]

Hi again Gabby,
I wouldn't recommend using a drill bit with the seat cutting tool. The reason for this is because the drilling and reaming process is the root of the problem with misalignment of the seat and guide hole. With these small engines there's not enough rigidity in the drill and if wanders just a little then the guide hole will be a little off. This problem is compounded if the drill tip is not perfectly uniform. The idea behind this tool is that: 1. It uses a guide rod that is a very close fit to the guide hole, 2. The area below the guide rod is substantial enough to prevent flexing and 3. you only want to kiss of the smallest amount of seat area with no chatter. This tool is used by hand not under power.
gbritnell

 

[Paulsv]

This tool is used by hand not under power.
gbritnell

George, if it is used by hand, and if it's used for cutting brass, is it necessary to harden the tool? Thanks for reposting the drawing!

 

[gabby]

Hi George, I somehow thought that it would not get past the scrutineers :hDe: and yes I get the point and I can understand your description of how the reamer works, many thanx.
Gabby.