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Post by jetjeff on Aug 28, 2016 10:12:05 GMT -5
Hi Smithy,
I wish I could find somebody with a turbo balancer to balance my homebuilt rotors, but they won't do it. There is one guy that will do it, but he's about a 6 hour drive one way.
Jeff
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Post by smithy1 on Aug 28, 2016 15:21:33 GMT -5
Hi Smithy, I wish I could find somebody with a turbo balancer to balance my homebuilt rotors, but they won't do it. There is one guy that will do it, but he's about a 6 hour drive one way. Jeff I'd be happy to balance your rotor for you, takes ~1 hour ....but being on the other side of the world makes things a bit difficult. Cheers, Smithy.
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Post by jetjeff on Aug 30, 2016 16:09:25 GMT -5
Hi All, Some assembly pics. I had to make a short temporary shaft extension for the front of the shaft as the front bearing spigot wasn't making contact with the front bearing while the rear bearing was making contact with the shaft tunnel. Getting all the holes aligned will prove difficult. Jeff
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Post by jetjeff on Sept 5, 2016 15:06:40 GMT -5
Hi All, I pressed the shaft in today. Bad news, there is WAY too much rotational resistance. Not sure if this is due to excessive interfearance fit or not. Warming the turbine area and compressor diffusor (with a Monocote heat gun) does seem to help some. I can spin it up to pretty high speed using compressed air. Thoughts? Advice? On the plus side turbine clearance is .013 to .016" range, thats exactly what I was shooting for. Jeff
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Post by smithy1 on Sept 5, 2016 16:28:05 GMT -5
Hi Jeff, What size bearings are you using....and what sort of bearing "pre-load" do you have??
My little turbines use 0.004"-0.006" tip clearance, anything more and they tend to get a bit warm.
Cheers, Smithy.
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Post by jetjeff on Sept 5, 2016 17:33:04 GMT -5
Hi Smithy,
The bearing are 28mm x 12mm, the are not angular contact full compliment, they are caged bearings grade 5, no pre-load. I'm wondering if GRW makes bearings this size?
Hmmm, I'm thinking a 3.40" turbine needs a little more than .004" - .006" tip clearance, IMO.
Thanks for the reply.
Jeff
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Post by smithy1 on Sept 5, 2016 18:47:02 GMT -5
Hi Jeff, 28x12....are sizeable bearings...and being normal ABEC-5 caged type bearings I'm not real sure they'll handle ~80,000rpm for too long, will be interesting to see how they go. GRW do indeed make 28 x 12 x 8 angular contact bearings for model turbine engines, (D6001/D604266) see here: www.grwbearing.com/products/high-precision-ball-bearings/ball-bearings-for-model-jet-turbines.html You could probably get away with 0.008"-0.010" tip clearance on a wheel of ~86mm dia. 0.013"-0.016" seems a tad high to me, I guess a lot depends on what materials are used etc......We do P&W PT6A engine hot sections here at my work and we use clearances of just 0.012" for turbine wheels of 8.5" (215mm) diameter as per the manufacturers dimensions fits & limits. Am really enjoying your build....keep it up...it's very interesting indeed. Cheers, Smithy.
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gtbph
Veteran Member
Joined: August 2013
Posts: 101
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Post by gtbph on Sept 6, 2016 2:19:10 GMT -5
Hi Jeff,
Does "No preload" mean that there is a sliding fit somewhere but no spring, or does it mean that there is an interference fit everywhere (both inner and outer races on both bearings)? If the latter, this could be the problem. The bearings have very little axial play so it would be easy to accidentally mount them such that they have in fact a very large "preload". The only other thing I can imagine is some kind of contamination in the bearings, but then I guess they would run very un-smoothly.
Alain
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Post by jetjeff on Sept 6, 2016 3:09:19 GMT -5
Hi Alain,
The bearings in this build are just standard deep groove bearings, they don't require preload, only annular contact bearings require preload supplied with a spring or wave washer.
I think the reason my rotor resistance is so high is, either I have too much interfearance fit (both I.D. and O.D.) or one of the bearings is slightly cocked. It's possible there is some contamination in the bearing too, not sure. These bearings are 'rated' for the 30k range, but this engine according to Schreckling would have a 'redline' of 50k or so.
My Old build engine uses GRW annular contact bearings, the rotor spins much easier.
Ugh, sometimes I feel like I take one step forward and two steps back,,,lol.
Jeff
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Post by jetjeff on Sept 6, 2016 4:30:12 GMT -5
Hi All,
Thanks for posting the GRW link Smithy.
Like I said before, heating the turbine with a heat gun reduces the resistance quite a bit. I'm not getting the engine anywhere close to it's running temp, it may be OK.
Jeff
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Post by jetjeff on Sept 6, 2016 16:09:47 GMT -5
Hi All,
I ordered some new bearings from Boca Bearing to replace the ones I have installed. They are ceramic balls stainless steel races, but grade 3 instead of grade 5. Reason being, is the interference fit is too tight for grade 5.
Jeff
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Post by jetjeff on Sept 7, 2016 4:27:28 GMT -5
Hi All,
Just for grins, I checked the turbine tip clearance on my Kingtech K-80, it appears to be at least .0075", maybe just a tad more. Smithy, you (I think) have one of these little beasties, maybe you could measure yours.
Jeff
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Post by smithy1 on Sept 8, 2016 18:04:11 GMT -5
Hi All, Just for grins, I checked the turbine tip clearance on my Kingtech K-80, it appears to be at least .0075", maybe just a tad more. Smithy, you (I think) have one of these little beasties, maybe you could measure yours. Jeff Yep...I have one, it's an old K80E, propane start, still runs great though....just put some feelers to it...average tip clearance is 0.0055"....varies a little depending on where in the NGV I measure, but only varies ~0.0015" or so. Cheers, Smithy.
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Post by jetjeff on Sept 10, 2016 10:09:17 GMT -5
Hi All, I disassembled the engine and removed the bearings. Still waiting for the new bearings to arrive from Boca Bearings. In the mean time I picked up an old leaf blower to use for starting. Jeff
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Post by jetjeff on Sept 13, 2016 15:42:27 GMT -5
Hi All,
I replaced the bearings with the new ones, still seems like a binding issue, not sure what to do next. The new ones spin a tad easier than the old ones, but no where near GRW bearings. I must have some issue going on with the bearings not being in the same plane. The new bearings are 28x12x8 and have ceramic balls, but there is no cage, they are full compliment. They do have a metal shield (where the rubber seal would normally go). Supposedly the shields are removable.
I'm stumped.
Jeff
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