Extra Dowel Machining Photos
08-05-08, 01:21 PM
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Extra Dowel Machining Photos
I hardly post too much anymore but I wanted to share some pics of some work that I'm doing to an engine. The engine is a 13B-RE, and 4 extra dowels are being added. Enjoy guys!!!
08-05-08, 07:33 PM
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Did you just add more factory dowels? They don't leave much support . RXBeetle has a nice right-up on making his own out of S-7 that were 9/16's OD and like 10mm ID. I've searched and searched for a commercially available hollow dowel that left more meat around the tension bolt and had limited success. Ultimately, I believe this is why adding four precision machined studs that fit like dowels, at the four corners of the engine, is what the pros do.
................... knocking on my head lol .................
08-06-08, 10:16 AM
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Lee: Thanks man, I have to admit, I was partially inspired by your pics in your buildup. I had heard of the process and machined it a hundred times, in my head, trying to find a reason why I couldn't get it done.
Correct my numbers if I'm wrong, but your making 780+ with only two extra pins? Thats pretty amazing.
Correct my numbers if I'm wrong, but your making 780+ with only two extra pins? Thats pretty amazing.
08-06-08, 11:15 AM
#6
The fact that the material around them is fairly thin isn't terribly relevant. Studs on the other hand don't strengthen at all. You need to understand the direction of each type of stress in an engine to understand why. Rotational stress (which come solely from torque) on the engine is supported solely by the dowel pins. By adding extra pins you are spreading this load out among additional points so even though the material in those places is reletively thin, the stresses on them aren't that high as instead of having the stress all placed at 8 points as stock (4 pins, 2 back to back, 2 ends each), all of the stresses will now be placed at those points plus the new points meaning the average stress for each location goes down considerably. If those locations were too thin, they'd fail.
Tension bolts only hold front to back separation stesses. Upgrading these will only strengthen rotational stresses if the bolts come into complete contact with the housings. If larger bolts are used and the housings all assembled as one unit and then the bolt holes milled out as a single unit each with a clearange of only a couple of thousandths (max) or better yet an interference fit over the bolts themselves, then they could contribute to rotational stresses. Stock they do nothing for this. Studs instead of bolts also do nothing to combat this. There is only one way to do it and very few do it that way yet think what they are doing is helping rotational stress.
A very simple way to make the engine a bit more resilient to these rotational stresses is to replace the 4 dowel pins (2 end to end each) with single long units that run the depth of the engine. This will spread the loads out across a greater area and allow less flex. Adding a couple more of these would be better still as long as they are full length. This is the proper way to do it. Tension bolts would be better replaced with studs as the studs will load at each end when tight rather than only at the thread end of a bolt. This too spreads stresses out across the engine.
I deal with stuff like this everyday at work with up to 3000 hp pumps that run up to 7500 psi of pressure and we need to take direction of stresses into consideration when designing various parts. What you might think will work just by looking at it may actually not in the real world as the directional loads may not do what you initially think they do. Working in this field has been very eye opening when it comes to my hobbies, particularly rotaries.
Tension bolts only hold front to back separation stesses. Upgrading these will only strengthen rotational stresses if the bolts come into complete contact with the housings. If larger bolts are used and the housings all assembled as one unit and then the bolt holes milled out as a single unit each with a clearange of only a couple of thousandths (max) or better yet an interference fit over the bolts themselves, then they could contribute to rotational stresses. Stock they do nothing for this. Studs instead of bolts also do nothing to combat this. There is only one way to do it and very few do it that way yet think what they are doing is helping rotational stress.
A very simple way to make the engine a bit more resilient to these rotational stresses is to replace the 4 dowel pins (2 end to end each) with single long units that run the depth of the engine. This will spread the loads out across a greater area and allow less flex. Adding a couple more of these would be better still as long as they are full length. This is the proper way to do it. Tension bolts would be better replaced with studs as the studs will load at each end when tight rather than only at the thread end of a bolt. This too spreads stresses out across the engine.
I deal with stuff like this everyday at work with up to 3000 hp pumps that run up to 7500 psi of pressure and we need to take direction of stresses into consideration when designing various parts. What you might think will work just by looking at it may actually not in the real world as the directional loads may not do what you initially think they do. Working in this field has been very eye opening when it comes to my hobbies, particularly rotaries.
08-06-08, 06:25 PM
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The fact that the material around them is fairly thin isn't terribly relevant. Studs on the other hand don't strengthen at all. You need to understand the direction of each type of stress in an engine to understand why. Rotational stress (which come solely from torque) on the engine is supported solely by the dowel pins. By adding extra pins you are spreading this load out among additional points so even though the material in those places is reletively thin, the stresses on them aren't that high as instead of having the stress all placed at 8 points as stock (4 pins, 2 back to back, 2 ends each), all of the stresses will now be placed at those points plus the new points meaning the average stress for each location goes down considerably. If those locations were too thin, they'd fail.
Tension bolts only hold front to back separation stesses. Upgrading these will only strengthen rotational stresses if the bolts come into complete contact with the housings. If larger bolts are used and the housings all assembled as one unit and then the bolt holes milled out as a single unit each with a clearange of only a couple of thousandths (max) or better yet an interference fit over the bolts themselves, then they could contribute to rotational stresses. Stock they do nothing for this. Studs instead of bolts also do nothing to combat this. There is only one way to do it and very few do it that way yet think what they are doing is helping rotational stress.
A very simple way to make the engine a bit more resilient to these rotational stresses is to replace the 4 dowel pins (2 end to end each) with single long units that run the depth of the engine. This will spread the loads out across a greater area and allow less flex. Adding a couple more of these would be better still as long as they are full length. This is the proper way to do it. Tension bolts would be better replaced with studs as the studs will load at each end when tight rather than only at the thread end of a bolt. This too spreads stresses out across the engine.
I deal with stuff like this everyday at work with up to 3000 hp pumps that run up to 7500 psi of pressure and we need to take direction of stresses into consideration when designing various parts. What you might think will work just by looking at it may actually not in the real world as the directional loads may not do what you initially think they do. Working in this field has been very eye opening when it comes to my hobbies, particularly rotaries.
Tension bolts only hold front to back separation stesses. Upgrading these will only strengthen rotational stresses if the bolts come into complete contact with the housings. If larger bolts are used and the housings all assembled as one unit and then the bolt holes milled out as a single unit each with a clearange of only a couple of thousandths (max) or better yet an interference fit over the bolts themselves, then they could contribute to rotational stresses. Stock they do nothing for this. Studs instead of bolts also do nothing to combat this. There is only one way to do it and very few do it that way yet think what they are doing is helping rotational stress.
A very simple way to make the engine a bit more resilient to these rotational stresses is to replace the 4 dowel pins (2 end to end each) with single long units that run the depth of the engine. This will spread the loads out across a greater area and allow less flex. Adding a couple more of these would be better still as long as they are full length. This is the proper way to do it. Tension bolts would be better replaced with studs as the studs will load at each end when tight rather than only at the thread end of a bolt. This too spreads stresses out across the engine.
I deal with stuff like this everyday at work with up to 3000 hp pumps that run up to 7500 psi of pressure and we need to take direction of stresses into consideration when designing various parts. What you might think will work just by looking at it may actually not in the real world as the directional loads may not do what you initially think they do. Working in this field has been very eye opening when it comes to my hobbies, particularly rotaries.
BTW, there are larger dia. studs, precision machined, that fit a precision machined hole that not only act as tension bolts but also as dowels. Would this path allow you to open up the oil passage? It's more work than I want to do.
I know the tension bolt is still a restriction. The tension bolt to dowel ID leaves a little to be desired. IMO.
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08-06-08, 10:51 PM
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Fred: Where've you been at ole buddy? Good to hear from you again. Your absolutely correct in your reply. While being machined, I noticed how thin some of the walls were getting, and initially, I said to myself they are way too thin. But after thinking a little deeper, we figured that the total rotational forces are going to now be spread out between 6 dowel pins per rotor, instead of just 2 per rotor, so there wont be too much force on them anyway, as long as our tolerences are kept correctly.
Per Rotor.
100% / 2 = 50% each
100% / 4 = 25% each
100% / 6 = 16.6% each
100% / 8= 12.5% each
100% / 10= 10% each
100% / 12 = 8.33% each
100% / 14 = 7.14% each
100% / 16 = 6.25% each
100% / 18 = 5.55% each
As you can see the more we added the less of an effect they had on simple math force distribution. Actual force distribution is higher on some dowels than others, so obviously we put the added dowels, where we THINK they would be needed the most. We stopped with 4 extra per rotor, so 6 total.
We actually considered machining one long hollow dowel to replace the upper stock dowels, and one long solid dowel to replace the lower stock dowels. It is still an option though.
Another backburner project we have is the stud kit were making. Its 17-4 ph stainless rod, .500" +.000 - .001. That should be plenty to even out the load between 18 studs.
Per Rotor.
100% / 2 = 50% each
100% / 4 = 25% each
100% / 6 = 16.6% each
100% / 8= 12.5% each
100% / 10= 10% each
100% / 12 = 8.33% each
100% / 14 = 7.14% each
100% / 16 = 6.25% each
100% / 18 = 5.55% each
As you can see the more we added the less of an effect they had on simple math force distribution. Actual force distribution is higher on some dowels than others, so obviously we put the added dowels, where we THINK they would be needed the most. We stopped with 4 extra per rotor, so 6 total.
We actually considered machining one long hollow dowel to replace the upper stock dowels, and one long solid dowel to replace the lower stock dowels. It is still an option though.
Another backburner project we have is the stud kit were making. Its 17-4 ph stainless rod, .500" +.000 - .001. That should be plenty to even out the load between 18 studs.
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