Ron’s Jowitt Popett Valve Engine

[Former MemberParticipant @formermember19781]

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[DiogenesIIParticipant @diogenesii]

Is this what you are after?;

Centre Finder for use in the Lathe Harold Hall

[Former MemberParticipant @formermember19781]

[This posting has been removed]

[JasonBModerator @jasonb]

Mine is the same principal except I put the sprung bit at the other end, will get some pictures of it apart for you in teh morning Ron.

[John BaronParticipant @johnbaron31275]

Hi Guys,

You really need to use an elephants foot on the dial gauge !

This is mine !

 

Edited By John Baron on 20/02/2020 21:04:46

[JasonBModerator @jasonb]

I've not found the need one you are not looking for a measurement just movement of the needle which will actually be magnified without the elephants foot so easier to see which way the work needs to move.

[JasonBModerator @jasonb]

Here you go Ron

main body has a Ctr drilled hole at one end, drilled 5mm at the other and partly tapped M6 to take the nut. Nut is reamed 3mm for the 3mm point that has a 5mm OD bush Loctited in place. Spring about Biro size or a bit heavier.

Drawing To Download

Edited By JasonB on 21/02/2020 13:46:34

[Ron LadenParticipant @ronladen17547]

Thanks guys and thank you Jason for the breakdown and drawing of your sprung centre I will get one made up.

Ron

[John BaronParticipant @johnbaron31275]

Hi Guys,

Actually anything long and thin with a point on one end will work just fine.

When I'm centring work, I hold the dial gauge in the tool holder. This means that I'm not having to translate vertical movements into horizontal ones.

 

Edited By John Baron on 21/02/2020 15:35:41

[John BaronParticipant @johnbaron31275]

Posted by JasonB on 21/02/2020 06:55:20:

I've not found the need one you are not looking for a measurement just movement of the needle which will actually be magnified without the elephants foot so easier to see which way the work needs to move.

An elephants foot doesn't magnify anything ! It just presents a parallel surface to a round object.

[JasonBModerator @jasonb]

But does it present a parallel surface as the rod is tilting up and down until level, it will allow you to measure the highest part of the rod.

Spring is there to stop the rod loosening or tightening as the work is adjusted therefore keeping the point in the hole.

[John BaronParticipant @johnbaron31275]

Hi Jason,

You can't have it both ways ! You are either looking for a measurement or an indication. With or without an elephants foot you will still get an indication.

[Quote] you are not looking for a measurement just movement of the needle [/quote] Your post.

The whole idea of using an elephants foot is that it provides a parallel surface to a round object. Though I do appreciate the exaggeration in your drawing to illustrate your point.

The idea of a long pointer is flexibility. A long thin pointer will follow the punch mark centre even if held rigid in a drill chuck at the tailstock end.

As far as a spring goes, yes I agree, it saves having to apply a little pressure to the tailstock wheel. My centre finder is simply a 10" inch length of 5 mm diameter rod, pointed at one end and dimpled at the other, no springs.

[Ron LadenParticipant @ronladen17547]

Jason,

I found a piece of 100mm x 50mm 6082 which I had tucked away and thought it would be ok for the cylinder, I can get the 80mm and 36mm out of it but unfortunately it is a tad short for the 64mm. Its actually 65mm but cut at an angle which means with cleaning up and squaring the ends I would just manage 62.5mm so the spigot would be short by 1.5mm at 2.5mm.

I thought of a couple of options to make use of it, take it back to 60mm and machine and fit a stepped spigot to achieve the 4mm or have a shorter 2.5mm spigot but I dont fancy that. One other option would be to maintain the 4mm spigot which would leave the cylinder block at 58.5mm, I couldnt see a problem with that in checking the drawings but thought I would check with you in case I have overlooked something.

Ron

[JasonBModerator @jasonb]

If you keep the cylinder head end the same and just shorten the cylinder so that you end up with the 4mm sipgot that would not be a problem, just means the cylinder mounting holes will be a bit nearer the edge and the front face of the cylinder won't quite line up with the curve of the base but a bit of file work would cure that if you were bothered by it.

Taking it off the cylinder head end could see the piston covering the transfer holes

As the piston does not come too far forwards another option would be to keep the main cylinder the correct length and cut a shallow recess then turn up a ring and loctite that in place to form the spigot.

[Ron LadenParticipant @ronladen17547]

I think I will go with keeping the cylinder the correct length and turn up a ring for the spigot.

Thanks Jason.

[Ron LadenParticipant @ronladen17547]

Made a sprung centre this morning ready for working on the cylinder, its a delux version in Magnesium Bronze.

[Ron LadenParticipant @ronladen17547]

The cylinder block is to size apart from adding a spigot ring, I machined it all on the mill using the 25mm end mill and its turned out nice and square so thats good.

Its now set up in the 4 jaw ready for drilling and boring, I know a recent thread said the proper way is to go from the pilot drill straight to the largest drill size but there is no way my lathe will cope with that so am going with a set of drills and do it in stages. I am going to give a 6.0mm, 13mm, 16mm, 19.5mm and 22mm a try, then bore out to the finished size 24mm.

I must admit I am a bit nervous about it I think the largest hole I have drilled on the mill to date is 13mm so I will see how I get on. One area where I may have a problem is the boring, the largest boring bar I have is 12mm with a GT insert which is probably too small but we will see. From 22mm to 24mm I only have to bore out 1.0mm so hoping a series of light cuts will work, but I dont know.

[Ron LadenParticipant @ronladen17547]

Well I need not have worried the drilling couldnt have gone better, sailed through it, none of the drills grabbed at all and the lathe had no problem.

[Ron LadenParticipant @ronladen17547]

I turned up a spigot ring as the alu block was just too short to allow the spigot to be turned from the end face. The spigot is fitted into a recess with 638 retainer and I have left enough meat for it to be turned to size.

Next job is boring the cylinder to 24mm, currently drilled to 22mm.

[JasonBModerator @jasonb]

That should work out OK Ron.

[Ron LadenParticipant @ronladen17547]

Thanks Jason,

Up early and turned the spigot to size and bored the cylinder using the 12mm bar (biggest I have) with a GT insert.

With a question mark over the size of bar I took it easy, 1.0mm to remove so went with 2 x 0.3mm passes, 1 x 0.2mm and 2 x 0.1mm all run at 650 rpm except for the last pass at 950 rpm. I may have just been lucky but as best I can measure using a Mitu Digimatic the bore is good to half a thou which over 60mm I am really pleased with.

[Ron LadenParticipant @ronladen17547]

Jason, thinking ahead a bit I see mention of the valve heads needing a good finish for seating, before I read that I imagined they would be lapped in but obviously there is no need.?

[JasonBModerator @jasonb]

They should seat themselves but if you find they leak than a bit of lapping won't hurt. With the engine running on a couple of psi it is not as critical as say the valve son an IC engine where you need the compression to get the fuel/air mixture to ignite.

With the long guide hole you may find the valve binds a bit if the drill has wandered so may also need to lap the stems or even open up the 4mm hole a fraction at the valve end. Also don't use too heavy an oil as that can make the valve drag and not close under the light spring prssure.

[Ron LadenParticipant @ronladen17547]

Thanks for the tips Jason, I have added to my build notes.

Ron

[Ron LadenParticipant @ronladen17547]

A bit more done, drilling, tapping and reaming next then on to my favourite part the shaping.

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