Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 129372 times)

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #165 on: August 11, 2015, 07:34:36 AM »
Fascinating work  :ThumbsUp:  :ThumbsUp: Still following along with interest  :wine1:
Best regards

Roger

Offline KB

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #166 on: August 11, 2015, 04:44:28 PM »

"Strictly Business" - the name says it all!

Your dedication to precision craftsmanship and knowledge of metallurgy is amazing.

- A friend of mines business motto; "...where quality is non-negotiable"

Thank you for taking the time to share all that you do.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #167 on: August 13, 2015, 02:46:16 AM »
I'm showing something a little different that  I have been working on for some time. Two .8966 or .9467 cu in, custom built engines, are precisely located in the bored mount to give the correct gear mesh. This is made possible with the precision, concentrically ground, OD's & ID's of the full hard AISI O-1 steel front ends which are located in the precision, jig bored, 2024 T-351 aluminum engine mounting blocks. Notice that the engines are securely fastened with 12, 8-32 screws, 6 on each side, tightened to 50 in lbs of torque. The 4, 8-32, FHSS on the top of the engine mount also clamp the center gear housing securely in place.

The gear ratio used is 1 to 1, which means the torque & HP are doubled at the propeller while the engine's RPM remains the same, minus any gear loses. Properly designed spur gears have an efficiency greater than 98%. (Dudley's Gear Handbook; 2nd edition; chapter 12) With each engine developing 7+ HP at 30,000+ RPM & 290+ in ozs of torque, at the propeller, there will be 14 HP at 30,000 RPM & 580 in ozs of torque. The engines are alternate firing & with the wine of the open gears, the setup sounds like a turbine when running.

The gears are made of "certified" unleaded 4340 prehardened (Rc-38) steel. This is the same material used for the gears in John Bridge's highly successful twin engine hydro named the "Led Sled". The gears have been proven to be highly wear resistant & run dry without any lubrication. I machined the gear blanks & the single split tapered sleeves in the same setup. This insured that all the gear internal tapers & all the split sleeve external tapers will match. North Shore Precision Gear & Tool cut nine gears plus two additional sizing gears that are .0002" over & under the nominal size. Only my gear blanks & my tapered sleeves were used to machine these gears with carbide gear hobs. Both engine gears turn in a clockwise direction by using custom made inverted drum valves in the engines, while the propeller shaft rotates counter clockwise, allowing the use of available left hand propellers. There is a substantial weight saving by having one stuffing box, one drive shaft & one strut.

The total weight of the pictured gears with engines is 5 lbs 12 ounces. The main shaft uses a solid 1/4" drive shaft system with ball & pin universals. The universals are a simple form of a constant velocity type universal joint. All the male, female & thrust washer pieces are made from AISI O-1 tool steel. Some pieces are used full hard & other pieces are used as a spring temper. All the technology, metallurgy & engineering used on this set up has been proven to be sound.

Jim Allen
« Last Edit: August 13, 2015, 01:43:52 PM by strictlybusiness1 »

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #168 on: August 13, 2015, 07:35:14 AM »
I see that these engines are watercooled. Do you use a pump for circulation or just scoops facing the direction of travel?
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #169 on: August 13, 2015, 12:25:13 PM »
Roger,

I use a propeller blast type system with metering plugs at the outlets. Here's a photo of a typical system. Position of the intakes & intake line sizes are important. These things are not dragging in the water; they are approximately 9/16" above the water line a maximum speed.

JA
« Last Edit: August 13, 2015, 12:29:09 PM by strictlybusiness1 »

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #170 on: August 13, 2015, 07:40:14 PM »
Thank you  :ThumbsUp:
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #171 on: August 16, 2015, 05:25:31 AM »
This is how I set up my Themeac, J-45 tool post grinder to finish both holes of the connecting rod. The grinders motor has ABEC 8, permanently greased, sealed, ball bearings & it turns at a load speed of 10,000 RPM. The spindle has the same ball bearings except they are preloaded. The pulleys used will allow the spindle to turn 26,000 RPM. The unique characteristic of the Themac is in it's ability to enable the center of the grinder's spindle to be placed on the center of the lathe's spindle. Notice how the grinding spindle can rotate to any position with it's mounting to the motors OD.

A preliminary check of the hardened steel arbor mounted in the independent 4 jaw chuck shows a dead needle on the .00005" Brown & Sharpe best test indicator. After clamping the fixture with it's mounted connecting rod, another check is made.

The D 1-4 camlock nose on this lathe allows for tooling to be mounted, removed & remounted without the loss of the dead zero. Cleanliness is crucial when using mounts such as this.

The finished surface has an 8 to 12 micro inch finish. A finish which is to smooth of a surface & to much radial clearance will encourage the rollers to slide as they rotate.

Jim Allen

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #172 on: August 16, 2015, 09:58:25 AM »
Thank you again Jim for your explanations  :ThumbsUp:

I must admit that I never thought of grinding the conrod in the lathe like this, but it makes sense - big time  ;D

Best wishes

Per

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #173 on: August 16, 2015, 01:34:31 PM »
Per,

This method ensures that every connecting rod has exactly the same center distance & both holes will be square to each other in two axes at the same time. Honing can give the correct size, round holes, but it will not correct any misalignment between the two holes. There is always some misalignment with slight distortion due to the machining & final heat treating processes. Very high RPM connecting rods need tight tolerances to prevent roller skewing, roller sliding & high wear. There is no bushing material used in the upper end of these connecting rods. They run with the connecting rod's material directly in contact with the crank pin's material. The radial clearance in the top end is .0001" to .0002". The radial clearance in the bottom end is .0003" to .0005".

Jim Allen
« Last Edit: August 16, 2015, 01:43:26 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #174 on: August 26, 2015, 10:41:45 AM »
I have completed the ID grinding of the upper connecting rod holes in our sample pieces. We hope that the time spent selecting a suitable through hardening alloy & the align grinding of both bores, will give us the necessary information to move forward on this project. These connecting rods will be tested with the double roller window retainers, which gives 16 rollers compared to the stock number of 9. The ID grinding operation of the upper end hole is done with a 1/4" diameter, Borazon wheel, which has a 1/8" solid carbide shaft. The grinders spindle is turning at 31,000 RPM. Notice how steady the .00005" indicator is during the grinding operation.

Jim Allen

Offline petertha

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #175 on: September 03, 2015, 05:55:53 AM »
Notice how steady the .00005" indicator is during the grinding operation.

Somewhere in this thread I asked a newbie question if you were somehow setting your compound at a very shallow angle in order to increment the grinder in small Y amounts rather than trying to split typical 0.001" dial increments going straight across the bed. This probably didn't make much sense to you & now I think I know why. Looks like you set up a DTI & just watch the needle advance so the compound can stay perpendicular, yes? Sheesh, that setup makes so much sense. And it serves double duty as a vibration meter :)

On an operation like this with hardened material, what is a typical amount of in-feed per grinding pass?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #176 on: September 05, 2015, 02:21:10 PM »
Sorry Petertha, but it looks as though I over looked this question. I normally use rigidly mounted, waterproof, shockproof, jeweled movement indicators to tell me exactly where things are positioned when using manual type machines that have vernier scales. I have learned that quality .00005" indicators, "DO NOT LIE" about the position or what is actually happening during a machining process.

The amount of out-feed for grinding an ID is never more than .001", which means an increase of .002" on the ID. Always grind so that the wheel can pass completely through & then traverse in the opposite direction at the same rate. Several spark out passes can be used to give a 6 to 8 micro inch finish on the ground surface when necessary. I use a sulfur based honing fluid for all my ID grinding. There should be very little heat generated during the process even though the wheel's RPM exceeds 26,000.

Jim Allen
« Last Edit: September 06, 2015, 01:15:06 AM by strictlybusiness1 »

Offline RcTintin

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #177 on: October 08, 2015, 01:55:30 AM »
Incredible work sir.

Please can you share more pics of your machine tools, jigs etc. Also, what lathe and mill do you use?

Fantastic thread, valuable information in here, thanks.


Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #178 on: October 15, 2015, 05:12:27 PM »
My shop is being re-organized as a result of purchasing a new house for the third time.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #179 on: December 04, 2015, 08:39:22 PM »
Incredible work sir.

Please can you share more pics of your machine tools, jigs etc. Also, what lathe and mill do you use?

Fantastic thread, valuable information in here, thanks.

The shop is coming along. All machines are in place & under power. Which particular jigs & fixtures are you interested in? There are hundreds of these things which are used to make the same part over & over again to the same tolerance.

Jim Allen
« Last Edit: December 04, 2015, 08:45:27 PM by strictlybusiness1 »

 

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