Author Topic: Strictly.... “ Hot Air “  (Read 71610 times)

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #255 on: October 23, 2018, 07:01:46 AM »
I used a vitron ring on my small one and it does not seem to have been affected by the heat.

Online Jo

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Re: Strictly.... “ Hot Air “
« Reply #256 on: October 23, 2018, 07:22:10 AM »
Thanks Jo, I’ll check those sources.
Have you started work on your platform casting?

Andy

:disappointed:

I'm still Log splitting  :facepalm:

I can't see me getting back into the workshop until Thursday at the earliest  :(

Jo
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Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #257 on: October 23, 2018, 07:26:59 AM »
I suppose if the grooves are already cut you need the same size as there is nothing to stretch them over and don't confuse the ID and OD :ShakeHead:

Also why look for odd sizes, just put BS 345 into google and get exactly the same size as Graham specifies

First hit

https://simplybearings.co.uk/shop/p512828/BS345-5.33mm-Section-100.97mm-Bore-VITON-Rubber-O-Rings/product_info.html

Though I usually use Sealforce

https://www.ebay.co.uk/itm/Imperial-Silicone-70-Shore-Rubber-O-Rings-5-33MM-Cross-Section-BS339-TO-BS365/322012190084?hash=item4af96c1584:m:mquNkdktn48uj7y_P5sUGNA:rk:6:pf:0
« Last Edit: October 23, 2018, 07:42:25 AM by Jasonb »

Offline Chipmaster

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Re: Strictly.... “ Hot Air “
« Reply #258 on: October 23, 2018, 10:09:46 AM »
Morning Jason, thanks for helping. I thought Simply Bearings £12.83 for two + post was a bit too much.
Before looking at your post I found a firm called Eastern Seals in Ashington, UK who appear to be able to supply BS345 silicone O rings at £0.59 each. Minimum order £5 so at that price I'll buy a few for spares. Graham might be interested in some too.

Andy

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #259 on: October 23, 2018, 10:18:43 AM »
I think the other two suppliers prices are about the same when you take off the "free postage" but if you can get several for the £5 minimum then they can no doubt post the lot for what the others charge for one.

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #260 on: October 23, 2018, 11:22:11 AM »
Whoa there, Neddy....

BS 345 when studying the tables is a 4" nominal ID with a 4,3/16" OD.... ONLY 3/16" thick!!

Further checking sees exactly what my original supplier said that at a 1/4" nominal thickness the starting
ID is 4,1/2" ....

As I posted yesterday perhaps they made a " special " batch as I did order over 100 units.

Cheers Graham.

Edit....

Following Jason's eBay link a metric, close equivalent is available at approximately 101mm ID with a 5.5mm thickness. But that's not a 1/4" either!!
« Last Edit: October 23, 2018, 11:29:21 AM by Alyn Foundry »

Offline Chipmaster

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Re: Strictly.... “ Hot Air “
« Reply #261 on: October 23, 2018, 11:44:06 AM »
Well the plans I followed specified a 3/16" BS 345 O ring, here's an extract from your plan that I photographed!!

Andy

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #262 on: October 23, 2018, 11:59:47 AM »
Hi Andy.

Well.... you can't argue with that, can you?    :lolb:

We did however use a different tack on later builds by only putting a 1/4 of the groove in each of the Iron parts to leave half the remaining thickness as a thermal barrier.

I'm not able to measure the last remaining " O " ring at the moment but will post the results later.

Cheers Graham.

Online Jo

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Re: Strictly.... “ Hot Air “
« Reply #263 on: October 23, 2018, 12:14:03 PM »
I just measured mine and it is 5mm diameter.

Jo
Enjoyment is more important than achievement.

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #264 on: October 23, 2018, 12:50:27 PM »
A nominal 3/16" O ring Which BS345is  has an actual cord diameter of 0.210" or (5.33mm for Jo)and her's sounds closer to that than it does to 1/4" Nominal which has a cord of 0.275" or 6.99mm

You could try a Metric 6mm ring which is a true 6mm cord and 100mm ID if you want to get close to 1/4" actual diameter

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #265 on: October 23, 2018, 03:45:47 PM »
Well....

It would appear that an apology is needed here, a " cap in hand " emoji etc.

The last " O " ring on stock measures a smidgen over 5mm, 5.2 to be precise.

I was absolutely convinced they were a 1/4" section, so you guys n gals, carry on regardless!!

Cheers Graham.

Online Jo

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Re: Strictly.... “ Hot Air “
« Reply #266 on: October 23, 2018, 06:03:36 PM »
Another set of Robinson castings have been discovered hiding in plain sight on my dining table :thinking:

They look very good quality (the foundry is somewhere on the Fens but that was all we were allowed to know ::) ) The pictures on the drawings and the instructions do not match. The pictures with the drawings suggest that there are two spinnings which there are not  :ShakeHead:  There is a very nice Brass engine plaque  :) Yes this is another very nice casting set from Polly Wobbles  :ThumbsUp:

Jo
Enjoyment is more important than achievement.

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #267 on: October 23, 2018, 06:45:52 PM »
The brass spinning for the displacer piston is not the best material as it conducts too much heat, make one from stainless. That is what Irish Dave did when I suggested it to him and what I did on Little Robbie, about 0.3mm wall or less will do nicely.

As a bonus Dave's stainless one tipped the scales at 34g rather better than the Polly one which was 93g
« Last Edit: October 23, 2018, 06:50:14 PM by Jasonb »

Offline ettingtonliam

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Re: Strictly.... “ Hot Air “
« Reply #268 on: October 23, 2018, 06:49:11 PM »
Another stupid question. I've machined the base casting apparently successfully, with no signs of the dreaded cold shut lines. Now I've just machine the undersides of the cylinder and bearing castings, taking off just enough metal to give a clean flat surface. The drawing shows a dimension of 1 25/62" (1.390") from the top of base to the centreline of the cylinder and crankshaft. In both cases, this would result in a bore which was markedly offset in the casting. Using a dimension of 1 5/16" gives a much better looking result.
1 25/64" looks an odd size, and it is that size for, presumably, a very good reason, but what that reason is, currently escapes me.
Can you see any problems if I lower off the centreline by 5/64"? The only issue I can see is if the ends of the levers operating the displacer rod end up too low and bash the top of the base. I can always put packing pieces under the cylinder and bearing castings if I have to.
Looking ahead to when its finished, do these engines 'self start' when heated enough, or do they need assistance for the first turn or so?

Online Jo

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Re: Strictly.... “ Hot Air “
« Reply #269 on: October 23, 2018, 06:56:54 PM »
I had to alter the bottom to the centre line of the cylinder on mine as well Graham said it did not matter the motion would take out the minor differences.

These engines are not self starting you need to give them a twirl

Jo
Enjoyment is more important than achievement.

 

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