Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 129586 times)

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #90 on: October 18, 2014, 10:51:35 PM »
I'm with Roger - serious stuff and serious precautions.

Quote
With a lead antimony anode of 1/4" diameter, the tank should be able to put on .001" to .0015" of chrome/ side.

Ohh - I got that wrong previously - I thought that the anode touched the cylinder walls.

Again thank you very much.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #91 on: October 19, 2014, 12:15:00 AM »
I'm with Roger - serious stuff and serious precautions.

Quote
With a lead antimony anode of 1/4" diameter, the tank should be able to put on .001" to .0015" of chrome/ side.

Ohh - I got that wrong previously - I thought that the anode touched the cylinder walls.

Again thank you very much.

One of the characteristics of any hard chrome plating tank is the inability of the system to plate when the distance between the lead antimony anode (positive) & the desired surface to be plated, the cylinder's ID (cathode), is large. For example, the ID of the cylinder bore which uses the 1/4" OD anode is approximately .805".  When plating a 1.125" ID cylinder bore, a 5/8" OD anode is used. One reason for this is because the standard, chromic acid/ sulfate bath, is not very current efficient. This means approximately 14% of the electrical energy is used to plate the chromium & 86% is wasted. It also means that the plating process is slow but reliable. The solution is relatively easy to make, analyze, & control with economical, of the shelf chemicals.

Jim Allen
« Last Edit: October 19, 2014, 03:42:26 AM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #92 on: October 19, 2014, 11:35:11 PM »
Hi Jim

Thank you for your answer.

Let me see if I got this info right. In the first example, you got 805-250 = 555 mill clearance and in the second, you got 1125-625 = 500 mill clearance between the anode and the cylinder wall. Does that mean the I should aim for some 500 mill (½") of clearance if (and when) I try to do some hard chroming ?

Does that clearance apply to all sizes ? - I'm asking because I might be tempted to do a bigger engine if I got success with the small size (though admittedly not in the near future - I need to start on the small engines first, but one can dream) ....

Best wishes

Per

Offline Allen Smithee

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #93 on: October 20, 2014, 12:09:58 AM »
Your "clearance" figures should be half that because the bore and anode dimensions are diameters, where the clearance is a radius.

AS
Quidquid latine dictum sit altum sonatur

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #94 on: October 20, 2014, 12:31:51 AM »
Hi Jim

Thank you for your answer.

Let me see if I got this info right. In the first example, you got 805-250 = 555 mill clearance and in the second, you got 1125-625 = 500 mill clearance between the anode and the cylinder wall. Does that mean the I should aim for some 500 mill (½") of clearance if (and when) I try to do some hard chroming ?

Does that clearance apply to all sizes ? - I'm asking because I might be tempted to do a bigger engine if I got success with the small size (though admittedly not in the near future - I need to start on the small engines first, but one can dream) ....

Best wishes

Per

The distance between the anode's OD & the cylinders ID is 1/2 the total diameter distances or approximately .250" of clearance. You will want to make this distance as small as possible & still allow for an adequate space for the chromic acid/ sulfate solution. For larger diameter bores it will be necessary to have several anodes or a machined cast anode. The anode could also be made in the form of a hollow cylinder closed at both ends. The anode I use for the 1.125" bore is cast in a mold & then machined to size.

The length of the anode with respect to the length of the cylinder to be chromed should not be longer or shorter in length. In this case, the anode must be longer to facilitate its mounting in the PVC sleeve. The addition of the outside brass sleeve, which extends below the bottom of the cylinder & the brass top piece, which extends above the top of the cylinder,  prevents the common dogbone effect (build up of chrome) that could takes place at the top & bottom edges of the cylinder without the brass pieces in place, since the anode is longer than length of the cylinder being chromed.

The PVC outer shell electrically insulates the anode from the cathode (cylinder) & positions it dead on center. The large lip on the top of the brass sleeve (cathode) sits directly on the two cathode wires. It is clamped into position with the top brass ring & the square PVC nut using a large amount of force.

Jim Allen
« Last Edit: October 20, 2014, 07:12:17 PM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #95 on: October 20, 2014, 06:32:08 PM »
Thank you very much for clarifying that.

As for my wrong use of the word clearance - sorry, but being dyslexic and not having English as first language is bound to get some errors in my writing from time to time.  ::)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #96 on: October 20, 2014, 08:44:24 PM »
I am planning a detailed explanation of how to make a very rigid, high mechanically reliable, wear resistant, three piece split or cantilevered type crank shaft for use in 7.5 to 30 cc size engines, operating at very high HP (7.5+) & RPM (30,000+) numbers. Metallurgy, fixtures, heat treating & machining techniques make it possible to produce very high quality crankshafts on manual machines with manual tools. The top two photos show two piece & three piece, pressed together crankshafts & one of the fixtures used to grind crank pin holes in the lathe, using a Themac tool post grinder. The ground crank pin holes ID's, are square to the crankshaft's journal, in two axes, with in .0002" total indicator run out, over 6.000" distance. Press fit amounts of the crank pins in their ground holes for both types are .0013"+. No crankshaft failures (cracking or twisting) thus far. Also, pressed in pins allow for the replacement of any worn crank pin, giving the assembled piece an infinite life.

Jim Allen
« Last Edit: October 31, 2014, 12:43:30 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #97 on: November 15, 2014, 05:53:29 PM »
Crankshafts that are to be used in high HP, high RPM,  miniature two cycle engines (2.5 cc to 30 cc) are usually made of 8620 or 9310 steel which is case hardened. However, there may be other types of steels that are used by Eastern manufacturers. These crankshafts can be one piece cantilevered types, two piece cantilevered types or three piece split types. From left to right in the photo; the first two one piece cantilevered crankshafts made of 8620, case hardened tool steel, had their .2812" diameter crank pins sheared off. The next three cantilevered crankshafts (two piece types) made of 9310 tool steel also failed when their .3125" diameter, pressed in crank pins, sheared off. Both types were .3750" X .5000". All two piece crankshafts use crank pins made of M-2 full hard tool steel. The press fit amount used is .0013" to .0015" & all crank pin holes have their ID's ground.

The last two crankshafts are made of AISI S-7 through hardened tool steel, with .3281" diameter (M-2 steel) crank pins. They have never failed. The AISI S-7 tool steel is through hardened in standard hardening oil & tempered at 600* F followed by air cooling at room temperature. The crank pin hole is carefully ground, after tempering, to give a .0013"+ interference fit. The hole is ground square within .0002" in two axes for a distance of 6.000".  The shock resisting S-7 tool steel at this temper has a tensile strength of 285,000 psi; a yield strength of 220,00 psi; a hardness of Rc 54 & a Charpy impact value of 219 ft lbs.

More to come.

Jim Allen



« Last Edit: November 15, 2014, 06:02:33 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 #98 on: November 15, 2014, 06:27:52 PM »
I'm still following with a lot of interest and some amazement  ::)

Some of the crank discs are left round with balance slots cut with something like a woodruff cutter. Does this offer advantages over the more conventional 'scalloped' designs?
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #99 on: November 15, 2014, 08:28:20 PM »
Roger,

In depth constant load type dynamometer testing told me that dog bone type crankshafts make less HP than full disc crankshafts in the engines I build, especially in the over rev range. This may not be true in all engines. However, full disc type crankshafts, with slots cut with a woodruff cutter, are more rigid than dog bone types, but they require the addition of Mallory metal slugs to get the counterbalance amount correct. I balance at 33% of the total weight of the piston, wrist pin & connecting rod assembly. This overbalance condition has very small second harmonic vibration issues & it does increase the crankshaft's inertia, which has several advantages to be explained latter.

Many of the problems with high HP, high RPM engines originates with aluminum crankcase flexing. I use full a hard AISI O-1 tool steel front end with my custom made ceramic hybrid bearings fitted. The crankshaft is designed so that it is mechanically fastened to the inner race of both front bearings. A sleeve which fits over the crankshaft fastens both inner races of the front bearings together once the flywheel is bolted in place. The front end's seal is machined onto that same sleeve. Crankshaft end play is set at .003" to .004" axial play with machined spring steel washers of various thicknesses. Even at elevated temperatures, the end play remains the same because all the parts; the crankshaft; the sleeve; the shims; the front end & the bearing races, ARE ALL MADE OF STEEL!  This type front end runs faster & longer than any aluminum setup.

Jim Allen

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #100 on: November 16, 2014, 07:25:42 AM »
Thank you for the explanation. Is 'Mallory metal' some type of heavy tungsten alloy?
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #101 on: November 16, 2014, 01:30:27 PM »
Mallory metal is machinable carbide. It is commonly used by engine builders to balance crankshafts. It can be purchased in different diameters & lengths ready to be used or machined to size as needed. The pieces in the photos are 11.18 mm (.440") diameter X 20 mm (.784") long & weigh 33.2 gms (1.171 ozs). They are machined shorter in length & peened in place on both sides of the crankshaft to prevent movement. Mallory metal is expensive! The 9 pieces shown in the photo cost approximately $70.00.

Jim Allen

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #102 on: November 16, 2014, 07:07:45 PM »
In a previous job we used a tungsten alloy just called 'heavy alloy' for collimators for industrial X Ray sets (up to 15 Million volts). It certainly was heavy and also expensive. I wondered if this was something similar.
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #103 on: November 16, 2014, 07:42:47 PM »
Mallory metal is primarily a Tungsten (W) alloy with a little copper (Cu) & nickel (Ni). Tungsten by itself is very difficult to machine. This is the reason for creating an alloy which is very dense but machinable. In fact it is denser than lead. The high cost is due to the tungsten content. I believe there are two metals that would be more dense than Mallory metal; depleted uranium & gold. Wonder how much it would cost for a few slugs of these?

Jim


Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #104 on: November 16, 2014, 07:50:45 PM »
DU may not be so expensive as it is effectively a waste product from the current nuclear industry. It is used for shielding isotope X Ray cameras and also as ballast weights in some aircraft.
Best regards

Roger

 

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