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Post by Johansson on Dec 13, 2023 0:24:45 GMT -5
Thanks for the link Richard, I guess a seamless thick walled pipe would work. I am "stuck" with 50mm diameter where the bearings sits since that is the largest standard ball bearing that is rated for >10.000rpm continous use, so given that I need a 5-ish mm edge for the bearings to sit against the hole through the 60mm pipe can´t be more than perhaps 25-30mm. Not much to gain in weight then, and since I can get a 60mm solid shaft practically for free from the local steel supplier I think I will go the easy route. |
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Post by enginewhisperer on Dec 13, 2023 14:36:32 GMT -5
if you can get away with a 50mm shaft, you can get 50mm hollow gokart axles in various wall thicknesses.
Otherwise, it should be possible to buy precision ground solid shaft.
I have used it up to 40mm diameter and it's very accurate for perfect bearing fits, etc.
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Post by Johansson on Dec 13, 2023 15:28:43 GMT -5
if you can get away with a 50mm shaft, you can get 50mm hollow gokart axles in various wall thicknesses. Otherwise, it should be possible to buy precision ground solid shaft. I have used it up to 40mm diameter and it's very accurate for perfect bearing fits, etc. Hmm, you said something there. Perhaps a 50mm shaft with steel rings drilled and threaded for locking screws is the best choice? Then I have a good bearing fit as you say, and the rings are used as the bearing stops, the same function as a turned down 60mm shaft but without the problem of turning opposing bearing surfaces on a long shaft. I honestly cannot understand how guys like RC-Don can plan a project, buy all of the stuff in advance and a couple of years later end up with the exact engine he planned for. During the JU-01 and 02 builds I must have made hundreds of design changes on the fly while the chips were flying...  Cheers! /Anders |
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richardm
Senior Member
Joined: June 2022
Posts: 411
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Post by richardm on Dec 13, 2023 16:40:43 GMT -5
Go kart shaft looks good indeed Just make sure it is seamless. Otherwise the welded seam will trow it out of balance Almost impossible to remove the weld material inside the tube on such a length.
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Post by slittlewing on Dec 14, 2023 3:07:38 GMT -5
Kart axles are designed to have quite a lot of flex for cornering grip and to unload the inside tyre allowing slip due to no differential. Hence them being mounted in spherical bearings, they are available in various “stiffness” from soft to hard as a tunable chassis parameter where people run a soft for wet weather, but all are thin walled.
Cutting down a truck or commercial vehicle prop shaft might be a better option, cheap secondhand and you would expect a decent level of balance?
Cheers
Scott
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Post by Johansson on Dec 14, 2023 16:57:04 GMT -5
No use brainstorming this any more, I´ll go for a 50mm solid shaft.
I picked up the bearings and clamps today, hopefully I can pick up the sheet metal and shaft during the christmas weekend.
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Post by andym on Dec 16, 2023 16:06:09 GMT -5
Bring on the build...... was going to mention linear roller baring shafts are good option for your engine, will be ordering some myself some, for part 2 expect to see some pictures soon ...... how are you starting the big ass engine |
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monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 400
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Post by monty on Dec 16, 2023 16:15:40 GMT -5
Anders,
This is going to be fun to watch! I'm a little frustrated being tangled in my mathematical underwear at the moment. I wanted to do some casting over Christmas break...but instead I'm stuck in theory land. I want to just shut off my brain and build something for therapy. I'll have to settle on living vicariously through you. I expect to see you hammering metal with a stone adz by the light of the moon wearing a dead animal pelt! ;-)
Bearing specs are.....flexible. You can't go by what's in the catalog. Based on most catalog numbers, jet engines are impossible. They have large single row deep grove ball bearings (with split races!!!) rotating at 10-15krpm. You can get away with quite a lot by using mist lube and hybrid bearings. Switch to turbine oil, or use one of the new 0W-15 auto oils.
Monty
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Post by Johansson on Dec 17, 2023 11:45:09 GMT -5
Bring on the build...... was going to mention linear roller baring shafts are good option for your engine, will be ordering some myself some, for part 2 expect to see some pictures soon ...... how are you starting the big ass engine Another big plus about a large engine, with an idle at 2500rpm a standard automotive starter with a one way bearing as clutch should work. The one way bearing should allow me to have the starter fixed on the shaft without a bendix clutch, when the engine starts pulling it should simply outrun the starter. For the initial tests I think I will use a 230V starter motor and a 230v hydraulic pump as fuel pump, that way I wont have to worry about batteries losing power during a run. |
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Post by Johansson on Dec 17, 2023 11:55:36 GMT -5
Anders, This is going to be fun to watch! I'm a little frustrated being tangled in my mathematical underwear at the moment. I wanted to do some casting over Christmas break...but instead I'm stuck in theory land. I want to just shut off my brain and build something for therapy. I'll have to settle on living vicariously through you. I expect to see you hammering metal with a stone adz by the light of the moon wearing a dead animal pelt! ;-) Bearing specs are.....flexible. You can't go by what's in the catalog. Based on most catalog numbers, jet engines are impossible. They have large single row deep grove ball bearings (with split races!!!) rotating at 10-15krpm. You can get away with quite a lot by using mist lube and hybrid bearings. Switch to turbine oil, or use one of the new 0W-15 auto oils. Monty Ha ha, I hope to delight you guys with some bronze age mechanics from the deep Swedish woods. In hindsight it was bad timing to change jobs just before I started on this build, at the old job I had full access to a complete sheet metal workshop which would have made this project soooo much easier. I´ve bought a sheet metal bender and some other stuff so I think I can get it done in my little shed instead. I agree on the bearings, and this engine will go through a barrel of kero faster than a community service lady finishes a bag-in-box wine on a friday evening, so even if increased revs will decrease bearing life by 10x I would be stone broke from fuel costs way before the bearings fail on me.... |
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monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 400
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Post by monty on Dec 17, 2023 14:38:44 GMT -5
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Post by Johansson on Dec 18, 2023 0:13:06 GMT -5
For a Scandinavian it is easier to relate to than gallons. |
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Post by Johansson on Dec 27, 2023 14:44:44 GMT -5
I filled the truck with sheet metal and steel chunks at the store today, so now I have some material to work with.
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Post by andym on Dec 27, 2023 14:48:54 GMT -5
I filled the truck with sheet metal and steel chunks at the store today, so now I have some material to work with. Nice..... |
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Post by Johansson on Dec 30, 2023 13:14:49 GMT -5
The shovel is in the ground so to speak, I made the first couple of hours on the engine today! First on the list was to make the centers for the turbine and compressor hubs, they will house the cone clamping elements and hopefully make a snug and un-wobbly (don´t think that is a word...) connection between the wheels and the 50mm shaft.  Here are the finished centers with a cone clamp fitted.  With the centers made I could weld them to the hub plates, they are 8mm thick steel that will hold both the double walled compressor and the turbine blades. I´ve made it like this for three reasons: 1. The hubs will be a non flexible part of the wheels that will ensure that nothing will start oscillating at 10.000rpms. 2. Since I will bolt the compressor bladed section and the turbine blades to the hubs it will save me lots of time if I need to redesign something. 3. It was the first idea that crossed my mind.  I sent Olov an SMS and proclaimed that Mobacken Racing finally has circled back to its roots, stick welding compressor wheels together. With a farmers mindset and a stick welder even the stars are within reach! Cheers! /Anders |
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