Author Topic: Strictly.... Hot Air  (Read 41720 times)

Offline Jasonb

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Re: Strictly.... Hot Air
« Reply #450 on: November 25, 2020, 07:32:11 AM »
Graham's method probably gives a taper that looks like a flight of stairs if you were to enlarge it enough with multiple points of contact for the key and it seems to work for him.

I tend to hold the bush in my vice so the slot is milled top to bottom using the Y axis so you have the top and bottom making contact with the vice jaws and then use a similar method to the key by packing under the vice, just don't over tighten it back down onto the table.

Depth of slot make it the same as the parallel bush at the point of entry eg just under the flange and getting deeper towards the end otherwise the broach won't enter the hole. If in doubt make it a bit deeper and you can always add a bit of shim under the supplied one. MAKE SURE YOU BROACH FROM THE CORRECT SIDE.

I usually oil the broach/bush when cutting CI

I think you said you used gauge plate for the key so this won't apply but if you do any with rectangular key steel in the future then leave the key on the length of stock right until last, that way you have something to pull it in and out with while checking the fit. Moles on the far end give you something to tap against to get it out without

« Last Edit: November 25, 2020, 07:37:12 AM by Jasonb »

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #451 on: November 25, 2020, 08:58:28 PM »
Jason and Graham,

Thank you for your advice.  I decided to go with Jasons option and make the tapered bush.  Setting up the taper was much easier this time.  Could not do it along the Y axis as the vice is just too big to manhandle, so went and used the support collar I had made.  All was going well till got down about 30thou when the 1/8" cutter I was using decided to shatter.  After much searching I found a new Clarkson cutter  (as opposed to the initial no idea where it came from cutter).  Slowed the cutter down and went very very slowly. 20th DOC each pass.

Tomorrow comes the acid test, broach the slot in the flywheel.

Colin

Offline Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #452 on: November 28, 2020, 04:47:44 PM »
Slot in flywheel broached nicely.  Its maybe little too deep (need to either take 15 thou out of bottom of broach guide or use a thinner shim.  It came with a 30thou.  I really needed a 15thou.  Reasonably happy for first ever keyway.

Used a length of 5/16" silver steel for the displacer rod.  Drilled and tapped the bottom for screw to hold the displacer piston, and then drilled reamed the cross-hole at the top to connect it to linkage.  I had found a really nice Eclipse 4" Magenetic V block on Ebay a few days earlier and it turned up Friday afternoon just in time to be used to hold the displacer rod for drilling/reaming.

The piston boss is made from 3/4" hex brass stock.  Put in 3 jaw on Myford and turned end down and then ran 2BA die up it.  Made a small silver steel mandrel and tapped it 2 BA.  This could then be mounted in collet chuck on dividing head on mill and the boss screwed into it.  Centered the boss and zeroed the DRO's, then turned dividing head through 90 degrees and set up to drill/ream gudgeon pin hole.  When drilled/reamed turned dividing head back to vertical and cleaned up the sides with 3/8" end mill and milled the centre out.  Cleaned up edges and ran reamer through to clean out and frays.

I had made gudgeon pin a few days earlier and just needed to cross-drill for split pin.  Decided this was going to be easier with tailstock drilling pad in the Cowells lathe.  Drilled out 1.7mm for split pin.

Next job is the bearing support.

I am still looking for suitable displacer piston, not managed to find the appropriate size of crabmeat tin.  I do have a sheet of 0.5mm stainless (and shortly some 1.2mm).  I am thinking of trying to make a piston from this.  How much does weight affect the piston. I assume it needs to be as light as possible.  Was thinking of 1.2mm for top and bottom and the sides from 0.5mm.  Wondering whether I can maybe glue the sheet to a board, and then trepan it out to size (85mm or just over) and whether feasible to turn the outer face down by 0.6 mill to act as a boss to locate in the stainless tube/cylinder.  Could punch the holes in top and bottom with 1/2" punch in the flypress, then hopefully few dabs of silver solder to hold together.  Does this sound feasible or am I in cloud cuckoo land.  I obviously need to source tin-can or make this prior to continuing with the hot end and main body.

Colin
« Last Edit: November 28, 2020, 05:21:20 PM by Twizseven »

Offline Alyn Foundry

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Re: Strictly.... Hot Air
« Reply #453 on: November 29, 2020, 11:33:53 AM »
Progressing nicely Colin.

Regarding the displacer piston, hang on for a couple of days. I shall be shopping at ASDA next Tuesday I'll have a look for you.

Cheers Graham.

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #454 on: December 14, 2020, 06:35:48 PM »
Been to my local ASDA and checked every tin of fish/crabmeat I can find.  At this point in time they do not appear to have the 145gm tin.  The nearest I can find is an ASDA Red Salmon 170gm.  This is 86.04mm diameter around the beaded end and 44.5mm tall.  The only problem is that it tapers down to the bottom of the can to as near as I can measure 78mm.

Is this too much of a taper to work.  Does it need a close fit at the top and bottom of the regenerator.  If so the only way I think I could use would be to remove the bottom of one can and the top from another and solder together where they touch and hope to get them lined up okay.  But would soft solder work, or does the hop end get too hot?

Colin

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #455 on: December 14, 2020, 09:52:43 PM »
Base and Hot End now machined.  Calculation for location of groove for 'O' ring was not perfect, but as machined as rounded groove I don't think it will matter hugely.  The final position is just a tad deeper than the the rest. 

Cannot decide whether to start hacking the salmon tin apart or machining the power cylinder and piston.

Colin

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #456 on: December 20, 2020, 06:36:22 PM »
Decided to have a go at the Regenerator/Displacement piston. Decided to try the ASDA Salmon tin.
I did not want to cut the tin open and have it deform in any way. Mounted it rim side down in the large indexer and centralixed it with coax centering tool.  I did not want to use end mills or wood hole cutters and then remembered I had bought a set of Parkside diamond hole cutters from LIDL a year or so ago.  Had a look at these and they were nicely sized so picked 1/2" one and put a hole in the centre.  It cut a nice clean hole.  Off set the indexer by 1" in the Y axis, set indexer to 72 degrees and worked my way round till I had a ring of 5 equidistant holes.  Then removed the juice the salmon was packed with with a small syringe with a large bore needle.

To ensure that the hole in what was to become the bottom was perfectly centered I put a long centering drill in chuck, went down through the salmon layer till touched the bottom of the tin.  As soon as I felt the drill go through I stopped.  Removed the tin from the chuck and looked at bottom of tin.  Realised I had cocked up slightly.  The base of the tin had sprung and and although I had stopped as it broke through it had sprung up and the centre drill had left a larger hole than required. :ThumbsDown:  Luckily I had prepared for such eventualities by buying a second can of salmon. :ThumbsUp:

Repeated the exercise only this time used a 3.5mm drill to give hole size required.

Turned the can over and repeated to put another 5 holes but offset 36 degrees to the set on the other side.

Then spend 15 minutes removing the contents of the can and throwing in the bin.  I did not think the cats would appreciate swarf from the diamond cutter in their tea. :)

So now we have a regenerator/displacement piston with no soldering (silver or otherwise).   :cartwheel: I now need to turn down the rod on which the displacer is fitted and make a small shouldered washer for the top of the can.  Will also put a thin sleeve inside to separate the stainless steel mesh from the rod location to aid assembly.

Next step is power cylinder.

Colin

Offline Dave Otto

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Re: Strictly.... Hot Air
« Reply #457 on: December 21, 2020, 12:32:47 AM »
That turned out quite well! Thinking outside the box or maybe the can. :lolb:

Dave

Offline Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #458 on: December 22, 2020, 01:52:05 PM »
To ensure displacer can be assembled and dis-assembled easily I decided to insert a sleeve in the centre with a support bush at the top and turn down the diameter of the rod to .250.  The sleeve also prevents the can from being crushed and miss-shaped when fixing screw inserted from the underside.  This worked okay and then assembled it and filled with two stainless steel pan scourer pads.

Graham just asked what it weighs so swiped the cooking scales of wife and checked.  125gms as it stands in the third photo.

Colin
« Last Edit: December 22, 2020, 02:29:58 PM by Twizseven »

Offline Alyn Foundry

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Re: Strictly.... Hot Air
« Reply #459 on: December 22, 2020, 03:07:46 PM »
Looking good Colin.     :ThumbsUp:

Here's mine.

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #460 on: December 22, 2020, 05:24:24 PM »
16 grams lighter.  Perhaps I should do some paring of weight.  Think I'll wait and see if works firt.

Colin

Offline ettingtonliam

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Re: Strictly.... Hot Air
« Reply #461 on: December 22, 2020, 05:44:07 PM »
I'm curious to know how you got the pan scourers in through those holes.

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #462 on: December 23, 2020, 01:06:13 AM »
Combination of stretching the scourer and handle end of old toothbrush, fingers and an Eclipse scriber. Fingers a bit sore by the end.  :)
Colin

Offline ettingtonliam

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Re: Strictly.... Hot Air
« Reply #463 on: December 24, 2020, 02:29:52 PM »
If you excuse the expression, is it well stuffed? I mean is the pan scrubber material in all the hard to reach corners? Presumably the more material there is in there the better the heat transfer will be?

Offline Twizseven

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Re: Strictly.... Hot Air
« Reply #464 on: December 24, 2020, 03:08:59 PM »
Definitely well stuffed  :Lol:

As I was feeding it in I was using the hooked end of a scriber to pull the contents internally around the can.  Filled it from two different locations.  It would be quite a struggle to get anymore in the can.

Colin