Cogsy
Well-Known Member
It's been a while, but from memory mine was perfectly smooth with no voids. Certainly turning the OD there were no apparent voids.
Machining Graphite
- Thread starter kiwi2
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BaronJ
Grumpy Old Git.
That seems more like what I would expect from an electric motor brush. The graphite would be more akin to a pencil lead.
My 2 pistons were both very dense with no voids. The first one was EDM graphite, & I thought that might be a little to hard. So I got regular graphite rod, & to tell you the truth, they seem close enough to be the same. The second piston is in it now. Two pics of the original if this works from my phone! Couldn't the the pics into the computer!
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Thanks for the replies. It looks like my graphite is not the greatest quality. It could be a grade meant for electrodes or molten metal stirrers.
I'll persist with it though and see how I get on. I'm intending to replace the brass displacer bush with a graphite one as Jim has done.
Regards,
Alan
I'll persist with it though and see how I get on. I'm intending to replace the brass displacer bush with a graphite one as Jim has done.
Regards,
Alan
Cogsy
Well-Known Member
I may have got lucky, but I bought mine as a graphite stirring rod off eBay.
Sorry for the very late reply and thread necro.
I got my Graphite rod from the following link. It's sold for Stirling engines but I'm using it for hybrid rocket motor nozzles.
Good price and the shipping to West Oz was very reasonable.
http://www.model-engine-plans.com/partskits/miscsupplies/index.htm
I got my Graphite rod from the following link. It's sold for Stirling engines but I'm using it for hybrid rocket motor nozzles.
Good price and the shipping to West Oz was very reasonable.
http://www.model-engine-plans.com/partskits/miscsupplies/index.htm
Hi All,
Success! I've got my Stirling engine running.
I started with the piston which I had made from aluminium. I polished it and found it met Jim's criterion in that it stayed suspended in the cylinder with my finger blocking the bottom and fell freely when I allowed the trapped air to escape. I therefore decided to leave it and not to replace it with a graphite one.
I did replace the displacer bushing with a graphite one, but found it to be no better than the brass one. This may be due to the graphite I purchased which was porous and I suspect of a grade more suited to an electrode. I managed to damage it by scraping the inside with the end of the displacer shaft so I put the old brass one back in.
I then found two problems which turned out to be the reason the engine wouldn't work.
The first of these was that I had put a layer of gasket goo between the upright holding the displacer and the base. There is a passage which goes from the displacer down the upright and along the base to the cylinder. It turned out that the sealant had oozed across the hole and had blocked off about 80% of the passageway. I cleaned it out and screwed the upright back onto the base without a sealant.
I tried running the engine and I could see it was trying to run but couldn't quite get there. I remembered Jim saying that some people could only get their engines to run using a blowtorch so I added an LPG torch to the mix and actually got the engine to run for the first time. It wouldn't run on just the alcohol burner however.
When it was running however I could see another problem. Both the displacer and the piston con rods run off the same shaft on the cam with virtually no clearance between them. This isn't a problem if everything is perfectly square but my engine wasn't and the con rods both wandered backwards and forwards on the shaft and were interfering with each other. I modified the con rod to the displacer to give some clearance between the two, and hey presto, the engine worked fine on just the alcohol burner.
So the engine has now migrated from a box labelled "STIRLING ENGINE - FAILED" where it has sat for the last couple of years, to the display cabinet in my lounge.
Thanks for all the helpful suggestions.
Regards,
Alan C.
Success! I've got my Stirling engine running.
I started with the piston which I had made from aluminium. I polished it and found it met Jim's criterion in that it stayed suspended in the cylinder with my finger blocking the bottom and fell freely when I allowed the trapped air to escape. I therefore decided to leave it and not to replace it with a graphite one.
I did replace the displacer bushing with a graphite one, but found it to be no better than the brass one. This may be due to the graphite I purchased which was porous and I suspect of a grade more suited to an electrode. I managed to damage it by scraping the inside with the end of the displacer shaft so I put the old brass one back in.
I then found two problems which turned out to be the reason the engine wouldn't work.
The first of these was that I had put a layer of gasket goo between the upright holding the displacer and the base. There is a passage which goes from the displacer down the upright and along the base to the cylinder. It turned out that the sealant had oozed across the hole and had blocked off about 80% of the passageway. I cleaned it out and screwed the upright back onto the base without a sealant.
I tried running the engine and I could see it was trying to run but couldn't quite get there. I remembered Jim saying that some people could only get their engines to run using a blowtorch so I added an LPG torch to the mix and actually got the engine to run for the first time. It wouldn't run on just the alcohol burner however.
When it was running however I could see another problem. Both the displacer and the piston con rods run off the same shaft on the cam with virtually no clearance between them. This isn't a problem if everything is perfectly square but my engine wasn't and the con rods both wandered backwards and forwards on the shaft and were interfering with each other. I modified the con rod to the displacer to give some clearance between the two, and hey presto, the engine worked fine on just the alcohol burner.
So the engine has now migrated from a box labelled "STIRLING ENGINE - FAILED" where it has sat for the last couple of years, to the display cabinet in my lounge.
Thanks for all the helpful suggestions.
Regards,
Alan C.
