453 replies to this topic

[Alan Draht]

The outside scribed circle on the spur gear or rear axle hole represents a 1-5/16" diameter wheel/ tire.

 

Per 1966 dragster class rules, the maximum allowed  tire diameter is 1-3/8", so a 1-5/16" diameter tire is a reasonable size to base the Husting and Maldonado gear guard size on.

 

The gear guards' outer spur gear circumference/ diameter must be less than 1-5/16" or the rear end of the car will bottom out on the track's surface.

 

The gear guards' "ring" of 0.10" thick magnesium material around the 69T gear is extremely slender.

 

 

 

 

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[Alan Draht]

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[Alan Draht]

The inside edge of the gear guards' spur gear cut out is complete.

 

After re-positioning the workpiece so that the pinion gear shaft's center is aligned with the rotary table's center, milling of the gear guards' pinion gear cut out begins.

 

 

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[Alan Draht]

A 1/16" diameter end mill is used to cut the gear guards' pinion gear opening.  A 1/8" end mill was used to cut the larger diameter spur gear opening.

 

 

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[Alan Draht]

As with the spur gear opening, a "bridge" of metal is left remaining between the pinion gear shaft center and the main workpiece.

 

Both the spur gear and the pinion gear centers and their links to the surrounding workpiece are preserved until the milling process is complete.

 

When the gear guards are 95% complete, the spur and pinion gear centers aren't needed any more to precisely re-position the gear guard assembly in alignment with the rotary table's center for the various steps involved with milling this complex part.

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[Alan Draht]

Checking the fit of the largest spur gears -- a 69T and a 70T -- against the gear guard's spur gear opening.

 

Same process with checking the largest pinion gear -- a 27T -- against the gear guard's pinion gear opening.

 

Both gears look like they will fit within their round openings.

 

 

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[Alan Draht]

It's time to move forward with cutting the outside edge of the gear guard to fit the Husting dragster's set-up.

 

The second gear guard is designated for the Madonado dragster.  The outline of its shape at the pinion gear end is smaller than the Husting gear guard's.  Its outline fits within the Husting gear's outline, so it can be milled further to achieve its final shape.

[Alan Draht]

Milling the outside edge of the spur gear's section of the gear guard...

 

 

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[Alan Draht]

Complete...

 

 

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[Alan Draht]

Test-fitting a 1-5/16" diameter tire on the completed spur gear section of the gear guard...

 

Rear end of the gear guard:

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[Alan Draht]

Bottom of the gear guard...

 

There is a very slight amount of clearance between the bottom edge of the gear guard and the tire's edge.

 

In other words, there is a very slight amount of clearance between the bottom edge of the gear guard and the track surface:

 

 

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[Alan Draht]

Top of the gear guard:

 

 

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[Alan Draht]

The assembly of two gear guards machined from stacked pieces of 0.10" thick magnesium will be un-bolted at this point in the fabrication process.

 

Each gear guard will be milled separately going forwards.

 

That's because the Husting and Maldonado dragster's frames are quite different from one another and their respective gear guards are too.

 

The shape of each dragster's gear guard forwards of the wheel axle/ spur gear section must be milled to match the Husting and Maldonado frame designs.

 

That includes matching the different approaches the each original builder took to attach his gear guard to the left side frame rail.

 

The Husting dragster's gear guard will be milled to match the drawing.

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[Alan Draht]

I knew going into this project that the gear guards of the Husting and Maldonado dragsters barely cleared the track surface.

 

It's evident in the photos.

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[Alan Draht]

Here's where things stand with the Husting dragster's gear guard as of this morning.

 

I should be able to finalize the gear guard's shape and mount it to the right side of the car later today.

 

 

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[Alan Draht]

This was a test fit of the gear guard.

 

The gear guard was installed on the rear axle and pinion shaft.  It fits perfectly.

 

I have more filing to do on the rectangular interior section of guard to get it to fit tightly over the motor's right end plate which carries the pinion shaft.

 

Then the guard will be attached to the end plate and the magnesium frame using two 0-80 bolts in holes that are tapped and threaded all the through the guard, the end plate and the magnesium frame.

 

Per Gene Husting, this strengthens the end plate and the assembly in general.   

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[Alan Draht]

The camera lens distorts the image, making the 69T spur gear appear much smaller than the gear guard.  In actuality, there isn't much space between the two parts.

 

 

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[Alan Draht]

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[Alan Draht]

And yes, the gear guard is within a hair's breadth of touching the track surface when 1-5/16" diameter tires are mounted on the car.

 

1966 dragster class rules state that rear tire diameter cannot exceed 1-3/8".

 

Gene Husting filed a small flat spot on the bottom of his gear guard to provide a little daylight between it and the track surface.

 

Rear tires for both the Husting and the Maldonado dragsters will have to be ground to a diameter which is just under the 1966 class maximum of 1-3/8" to ensure that there is sufficient ground clearance for racing while remaining technically legal.

 

Rear tire size cannot be at or less than 1-5/16" diameter or the gear guard may bottom out.

 

So, there's less than 1/16" to play with using the gear guard.  Nice.  

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[Alan Draht]

The Husting dragster's gear guard is complete.

 

The final stages of fabrication looked like this...

 

 

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[Eddie Fleming]

Alan

 

I understand you are doing a replica of a great car and that dictates the gear guard.

 

I ask myself why did it need a gear guard in the first place?

[Alan Draht]

This is the completed gear guard installed on the car...

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[dc-65x]

Alan

 

I understand you are doing a replica of a great car and that dictates the gear guard.

 

I ask myself why did it need a gear guard in the first place?

 

I believe it was to keep the parachute material used to stop the cars from getting caught up in the gears Eddie.

 

Nice job Alan. That's a lot of work!

[Martin]

Man, that is close to the track. I guess there was no minimum track clearance rule then. You may leave your mark at Mikes new track?

Following your epic build. Remember you saying the gear mesh was too tight. Did you mention the fix for that? 

I am always nervous about fixed gearing, but I get they did it that way.

[Alan Draht]

I'm not done with building this car yet, but I think that the most difficult parts are behind me.

 

The gear guards for these cars are -- to me -- the most difficult parts to machine.  Accuracy and precision is required every step of the way.

 

The 1966 era dragster's gear guard is my least favorite part to make.

 

The ring around the spur gear is very fragile.  It can easily be broken during the milling process.

 

The further along you get in fabricating this part without making any mistakes, the higher the risk that you'll screw up in the last few steps, including just drilling, tapping and bolting it onto the chassis.

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