Author Topic: Another breath engine (Huff and Puff)  (Read 1893 times)

Offline Roger B

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Another breath engine (Huff and Puff)
« on: April 06, 2019, 01:56:28 PM »
I have been inspired by Doc's start and Marv's version of the Huff and Puff and will make a version. I need to convert the drawings to metric and a have a question regarding imperial dimensioning conventions. The drawings from Doc's link use imperial fractions, imperial decimals and number drill sizes. The number drill sizes seem obvious, you use that size drill.  For other dimensions fractions and decimals are used, the crankshaft is 0.0625" and the hole in the flywheel is 1/16". Are fractions used for stock sizes and drill sizes and decimals for machined sizes? Am I reading too much into this?

The metric conversion will require some thought regarding the port sizes and positions and the dimensions of the piston valve to maintain the timing.
Best regards

Roger

Offline Florian Eberhard

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Re: Another breath engine (Huff and Puff)
« Reply #1 on: April 06, 2019, 02:06:09 PM »
Hi Roger

I have got a conversion table flying around from my stuart feed pump build - i could scan it and send it to you if you want?

Florian

Online Jasonb

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Re: Another breath engine (Huff and Puff)
« Reply #2 on: April 06, 2019, 02:21:39 PM »
Quite often on imperial drawings fraction and decimal are both used as a way of indication tolerance, with the decimal needing to be a tighter tolerance than the fraction.

In practical terms for an engine like this then silver steel/drill rod or ground mild steel will do for the shaft as that is likely to be off the shelf and close to 0.0625"  size. Most won't have a 1/16" reamer so the hole can be drilled with a 1/16" drill and the flywheel loctited to that.

In your case you will be better off using nearest stock sizes for both these items that doing a direct conversion so 1.5mm rod and a 1.5mm drilled hole will do.

Alternatively if you have a bit of lung capacity to spare then a simple way to do it is to allow 1/32 or 0.03125" on the drawing to equal 1mm which will give a slightly larger engine but most sizes will be in 0.5mm or 1.0mm increments.

Offline JC54

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Re: Another breath engine (Huff and Puff)
« Reply #3 on: April 06, 2019, 08:02:06 PM »
Hello all, I have just converted a simple beam engine (Beam engine with a twist) from imperial to metric and as Jason says go to the nearest available metric sizes for shafts and fittings. Doing it this way saved me a lot of problems, head scratching and frustration. Perhaps not strictly correct but some dimensions I left until engine was nearly built and made parts to fit..  ::) I wish I could understand this CAD stuff. John :old: :DrinkPint:

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #4 on: April 07, 2019, 08:20:42 AM »
Thank all for your feedback  :ThumbsUp:

Florian, thanks for the offer however I have a copy of Harold Hall's Metal Worker's data Book which has conversion charts and details of the American threads.

First thoughts:

Cylinder bore 1/4"  6mm
Valve bore 1/8"     3mm
Piston rod 3/32"    2.5mm Is this a bit large for a 6mm bore?
Crankshaft 1/16"   1.5mm Would 2mm be a better choice?
Fixings 0-80          M1.4 

I can adjust the piston stroke (1/4") and the valve stroke (1/8") to keep the port and valve geometry correct.
Best regards

Roger

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #5 on: April 07, 2019, 02:28:08 PM »
I have started to set out the cylinder block and valves. I had to change the port angle from 45░ to 40░ to compensate for the slightly greater distance otherwise both ports would have been connected to the inlet at the same time. With the valve in mid position both ports are slightly open to exhaust. Is this sensible or should I adjust the dimensions to have everything closed at mid position?

PDF attached
Best regards

Roger

Online Jasonb

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Re: Another breath engine (Huff and Puff)
« Reply #6 on: April 07, 2019, 02:47:37 PM »
You could reduce the distance between the piston and valve bores to compensate for the reduced diameters which should allow you to keep the angles the same and therefore the openings. off the top of my head the 7.5mm would come down to about 7.25mm

2mm piston rod should be ok

Offline bent

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Re: Another breath engine (Huff and Puff)
« Reply #7 on: April 08, 2019, 07:34:22 PM »
Y'all are pretty short winded...my son can blow hard enough to run my PM #3 (3/4 bore and stroke).  Of course, he's a trombone player ::)

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #8 on: April 12, 2019, 03:27:38 PM »
Thank you Jason. It all comes down to where I make the changes. If I change the bore centers I may have to change the crank/eccentric as well. I may end up doing this anyway  :headscratch: If I reduce the piston rod to 2mm I will probably have to change the little end (as George has done). A 0.8mm slot in a 2mm is possible but a little tight. I will draw up some more this weekend and see what it looks like.
Best regards

Roger

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #9 on: April 14, 2019, 07:53:01 PM »
I had a look at reducing the centers to keep the original port length and this seemed to give reasonable timing (PDF below). I thought about the little end and decided to try putting the 0.8mm tang on the piston rod and making a 2mm square slotted end on the con rod. Having drawn it could I make it? I took an small piece of 2mm thick brass, marked it out, drilled the little end 1mm and drilled and reamed the big end 1.5mm. I tried to cut the slot with a 0.8mm slitting saw but ended up with a slightly off center ~1mm slot  :facepalm:
The next step was to mill either side of a piece of 2mm stainless steel rod to produce a 0.8mm tang. That went OK as did marking and drilling a 1mm hole. The trial assembly was not so good, the 1mm hole in the conrod was 1.2mm one side and around 1.1 the other side  :(
I will try again with a 0.5mm slitting saw and starting with a 0.8mm hole.
Best regards

Roger

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #10 on: April 16, 2019, 07:51:22 PM »
I tried plan B for the conrod using the other half of the piece of brass. The slot was slightly under 0.8mm and central  :) The sides were then milled down to give a central thickness of 1.5mm. This could have been the original of 1.6mm (1/16"). One side of the little end was milled to size and the rod was cut away from the supporting piece. The other side was milled to size and with a little bit of work on the slot it all fitted together nicely  :)  :wine1:
Best regards

Roger

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #11 on: April 16, 2019, 07:57:18 PM »
As the Hobbymat was in milling mode I used my Proxxon FD150 to turn some 4mm od 1.5mm bore filling buttons to finish the big end and sides of the conrod. These were hardened and then clamped together around the big end with a short length of 1.5mm silver steel in a tool makers clamp. The big end and the sides were filled to shape. So small  ::)
Best regards

Roger

Offline Admiral_dk

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Re: Another breath engine (Huff and Puff)
« Reply #12 on: April 16, 2019, 09:19:59 PM »
I knew from reading here about the builds of this engine that it is small - but seeing the conrod on your thumb nail really brings the size into context  :ThumbsUp:

Nice work Roger.

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #13 on: April 20, 2019, 07:03:17 AM »
The cylinder blank, 11 x 11 x 20 was milled from 12mm square brass bar. The frame, 19 x 28 x 27.3 was cut to size from a bit in the offcuts box. The cylinder was set up in the 4 jaw independent chuck for drilling and reaming the piston and valve bores. I used a floating reamer holder as I have one. The frame was then set up, taking care due to the slightly different sides and the piston rod hole was drilled and reamed 2mm. Next the spigot that locates the cylinder was turned to 6mm.
Best regards

Roger

Offline Roger B

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Re: Another breath engine (Huff and Puff)
« Reply #14 on: April 20, 2019, 07:07:48 AM »
Next the piston rod was cut to length and threaded M2. The piston was turned from 7mm brass rod tapped M2 and Loctited onto the piston rod. It was finished to 6.2mm, the final sizing being done with it fixed to the rod to ensure concentricity.
Best regards

Roger