Author Topic: Project Centaur  (Read 4876 times)

Offline redhouseluv

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Re: Project Centaur
« Reply #105 on: February 04, 2025, 12:23:54 PM »
Ah right got it - I was moving the mill table 1st without repositioning. I was wondering how to do this with the work held in the 3-jaw but I can't  I'll have to clamp to the R/T instead

I've been using my school geometry and have been puzzling over how you determined the 22 degree angle?
Best regards

Sanjay

Offline Jasonb

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Re: Project Centaur
« Reply #106 on: February 04, 2025, 01:05:05 PM »
To do it with yur old school geometry set the best way would be to draw it out over size say 4x larger. Draw the central 3/4" circle, then th etwo 3/8" ones that make up th eends and then a line that is tangent to the two circles. You can then measure that with a protractor.

You could also mark it out 1:1 on the part and just tweak the rotatry table until you cut to the line which is how Chris described it.

These days CAD makes it easy, the part is constructed in much the same way as described above, excess lines trimmed and you just click two lines (blue) and it will tell you the engle.

Offline redhouseluv

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Re: Project Centaur
« Reply #107 on: February 04, 2025, 01:54:21 PM »
That's put me out of my misery .... I wondered if it was a pencil and protractor, but clearly CAD is king!

The machining worked (LHS side only) and although it is far from pretty and I understand how to complete this operation in future. My round stock was not quite the diameter required hence it looks truncated.

I will now attempt the actual piece, however, having looked at the carb, the fixing holes and exhaust port are all over the place and the size is larger than described on the drawing, so this will need some manual fettling

Thanks for explaining how to make lozenges!
Best regards

Sanjay

Offline redhouseluv

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Re: Project Centaur
« Reply #108 on: February 04, 2025, 09:07:48 PM »
This is the actual part, I used a combination of Chris' and Jason's methods.  I used a protractor and pencil to get the angle after drawing round the carb part and extended the lines out - 22 degs!  :)

Needed a fair bit of filing as the bolt holes were not evenly spaced  - needs a bit of emery and should be good
Best regards

Sanjay

Offline Admiral_dk

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Re: Project Centaur
« Reply #109 on: February 04, 2025, 09:28:48 PM »
That is a lot better - should increase your confidence quite a bit in relations to future use of same technique  ;)  :ThumbsUp:

Per        :cheers:

Offline redhouseluv

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Re: Project Centaur
« Reply #110 on: February 04, 2025, 10:22:01 PM »
Yes, Per, absolutely - its great to be shown how to do something and apply that knowledge straightaway. Thinking about all the things I've learnt on the forum since 2023, it's mind blowing especially as I was a late starter to machining engines which was the year before.

I need to learn more, I have a pile of projects!! ;D
Best regards

Sanjay

Offline redhouseluv

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Re: Project Centaur
« Reply #111 on: February 06, 2025, 01:47:03 PM »
The silver steel has arrived, so onto making the cutter......

I have drawn out the cutter using the measurements taken from both the drawing, but more importantly from the head itself.

There is small question around what I have called section B of the cutter, it is short in length as the 0.5" diameter section in the head has not been cut all the way down/near to the valve guide. I have tried to show this with an arrow in the pic and if you can see there is a crescent shape section which is where it hasn't been cut all the way down.

I don't think this is an issue as the valve guide is what will postion the cutter and there will still be 0.25" depth for the 0.5" diameter section?

Also I really don't want to risk damaging the valve seat or anything else by running a drill bit down the hole to remove this crescent shape if its not necessary
Best regards

Sanjay

Offline Dave Otto

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Re: Project Centaur
« Reply #112 on: February 06, 2025, 02:45:40 PM »
It seems to me that the section B is only to add rigidity by keeping the pilot as short as possible. You could omit it completely if it is going to be in the way, or as you have shown just make it short enough to fit.

Dave

Offline redhouseluv

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Re: Project Centaur
« Reply #113 on: February 06, 2025, 03:25:39 PM »
Yes, that's very true, in my drawing I've made 'B' slightly shorter than the measured distance as I did not want it interferring/preventing the cutting surface 'A' from contacting the valve seat.
Best regards

Sanjay

Offline Dave Otto

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Re: Project Centaur
« Reply #114 on: February 06, 2025, 03:52:07 PM »
Yes, and you also need to consider that when you cut the angle for the cutting edges it will drop even farther down.

Dave

Offline redhouseluv

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Re: Project Centaur
« Reply #115 on: February 06, 2025, 06:38:27 PM »
I have made an 'interesting' discovery whilst making the cutter.

- I couldn't work out why the cutter surface was not making contact with the valve seat (pic 1)
- I kept cutting section B down thinking it was hitting something, but no matter how much I removed, no contact (pic2)
- I think the valve seat has been so badly cut that there is a lip protruding on the farside on valve seat (pic 3)
- If you look at how the valve sits up currently on the seat the gap looks to be the same gap as the cutter in pic 2 (pic 4)
- The cutter diameter and valve's largest diameter are the same so it cannot be the the cutter is hitting anything else (pic 5 & pic 6)

I think this means the cutter is going to have to be used initially to remove the lip before it even makes contact with the seat. I think pic 3 of the lip tells the story visually without any measurements or tools being used
Best regards

Sanjay

Offline Jasonb

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Re: Project Centaur
« Reply #116 on: February 06, 2025, 07:06:32 PM »
You will have to watch how deep you go with that cutter, ideally you want the cutter a bit larger in diameter than the valve so that there is nothing for the side of the valve to come in contact with.

It may be better to set the head up on the mill slot facing upwards and flatten that whole seating area to remove any lip to a depth of say 0.320" lower than the ctr line of the valve guide, get it as near a right angle to the valve guide as possible.

The when using your seat cutter don't go right in to it's full 0.606" diameter

Offline Jasonb

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Re: Project Centaur
« Reply #117 on: February 06, 2025, 07:18:23 PM »
I mentioned early on that I thought the gap under the inlet flange was due to a tapered fit but Just looking at the drawings it is actually parallel so the flange should fit up tight to the head with a thin gasket. I was thinking of another engine that has it tapered.

Offline redhouseluv

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Re: Project Centaur
« Reply #118 on: February 06, 2025, 07:44:31 PM »
I understand, 2 separate operations:

- one to remove the lip going in through the 'front' using the mill
- second using the cutter for the seating

I've marked the area on the diagram in blue representing the lip and I think the distance 0.320" you have mentioned is the red arrow?

I can see that I'm going to have to proceed VERY carefully!
Best regards

Sanjay

Offline Jasonb

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Re: Project Centaur
« Reply #119 on: February 06, 2025, 07:57:37 PM »
that's it for depth. I was thinking of coming in from the cylinder side with say a 3/8" cutter and cleaning up the edge of the slot but suppose you could come straight down with a 5/8" one if you have it
« Last Edit: February 06, 2025, 08:03:42 PM by Jasonb »

 

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