453 replies to this topic

[Alan Draht]

Thanks everyone!  I wasn't expecting that.  You guys are great!  

 

Before I lay out what I think I need in the way of Weldun 64 pitch gears to build and race both dragsters -- Gene Husting's car and Manual Maldonado's car -- let me describe how a solution crystalized for me over the past 24 hours.

[Alan Draht]

I followed Husting's instructions for determining the distance between the axle and pinion centers.  I created a simple jig to test fit different combinations of pinion and axle gears.

 

To begin I used a Weldun 70 tooth gear, the closet thing I've got in size to Husting's 69 tooth gear, and a 23 tooth pinion, the same as Husting's pinion.

 

I first drilled the axle hole and placed the 70 tooth gear on a 1/8 - inch axle into position on the aluminum jig plate's surface.

 

I positioned a 23 tooth pinion gear in line and engaged with the axle gear, marked the hole's centerpoint, and drilled the other hole for the pinion shaft.

 

This is the result.  This 70 tooth / 23 tooth combination is the baseline condition.

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[Alan Draht]

I tried to put a 24 tooth pinion against the 70 tooth gear, but it clearly does not fit.

 

I tried to put a 22 tooth pinion against the 70 tooth gear, and the result (pictured below) shows that it fits, but the gear mesh gap is big and sloppy.  In action, the steel pinion would probably chew teeth off of the 70 tooth axle gear.

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[TSR]

Alan, in principle and as long as the gears were machined according to SAE spec, any spur gear should match any pinion of at least 11T, as the teeth of smaller pinions are going to be a compromise. Weldun was the finest slot car gear maker in the 1960s, so whatever you will try will have limitations, but a 69T VS o 68T or 70T should absolutely not matter... the mesh will be the same. Maybe the pinion needs deburring? Sticking it in the tumbler would likely do the job better than anything.

[dc-65x]

Hi Alan,
 
Here's a formula to determine the center to center distance of spur gears:
 

 
Turns out that a total of 63 teeth in a 64 pitch gear set would give me a gear spacing of .492" with the gears pushed tightly together. Setting them up with a little "sloppski" at a .500" spacing in my jig confirmed a perfect mesh.

 

Add the number of teeth for spur and pinion together and divide that by the pitch (64). Then divide that number by 2 and you've got a spacing with the gears tightly together. 

 

Also, as you've mentioned, you can use any combination of spur and pinion with the same total tooth count in that same spacing. A 10T and 50T will have the same center distance as a 30T and 30T. 
 

[Alan Draht]

The next size down from a 70 tooth gear that I have is a 66 tooth gear.  I tried that combination in the jig and the largest pinion Ive got, a 25 tooth gear, doesn't touch the axle gear.  If I had a 26 toot pinion and it fit properly, I'd end up with a gear ratio of 2.54 : 1.  This approximates the 2.6 : 1 ratio Gene Husting said he never went beyond.

 

At the other end of the spectrum, the limiting factor is the axle gear's size.  The gear guard is sized to fit close to the edge of the largest axle gear size used for this car, as well as the largest pinion gear size.   

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[Alan Draht]

Alan, in principle and as long as the gears were machined according to SAE spec, any spur gear should match any pinion of at least 11T, as the teeth of smaller pinions are going to be a compromise. Weldun was the finest slot car gear maker in the 1960s, so whatever you will try will have limitations, but a 69T VS o 68T or 70T should absolutely not matter... the mesh will be the same. Maybe the pinion needs deburring? Sticking it in the tumbler would likely do the job better than anything.

 

Thanks, Philippe!    

 

I was testing to see if a pinion gear size one up or one down from the 70 / 23 tooth combination would also fit okay between the fixed axle center-to-pinion center dimension. 

 

My testing seems to indicate that there is no tolerance between gears to do that.  If you go one tooth up in pinion size, you have to go one tooth down in axle gear size to fit properly within the fixed dimension.

[Alan Draht]

One more photo to illustrate the gear guard size limitation.  The gear guard is practically touching the ground.

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[Tom Katsanis]

Alan my dragster has run 1.28 geared 28/67 with a 6 volt modified ram motor at 3 to 1 the car did 1.5s.
The cars react differently on 16 v compared to 36 v my car with the 3 to 1 ran 1.17 on 30 volt.
Hope that is a help.

[dc-65x]

I have a 69T Weldun set screw spur gear that you are welcome to Alan.

[Uncle Fred]

Those gear guards were needed because we ran the cars into bunched up parachutes to slow them down. After a run it would still take some time to cut the silk out of the gears.  

[Alan Draht]

Hi Alan,
 
Here's a formula to determine the center to center distance of spur gears:
 

 

Add the number of teeth for spur and pinion together and divide that by the pitch (64). Then divide that number by 2 and you've got a spacing with the gears tightly together. 

 

Also, as you've mentioned, you can use any combination of spur and pinion with the same total tooth count in that same spacing. A 10T and 50T will have the same center distance as a 30T and 30T. 
 

 

Hi Rick,

 

Sorry for the delay in responding.

 

I want to thank you for providing that formula for determining the precise center-to-center distance between spur gears.

 

Using that formula for the 70 tooth axle // 23 tooth pinion assembly, the dimension is 0.7266 inches. 

 

I measured the center-to-center distance on the jig I constructed, and sure enough, it is 0.7265 inches!

 

I much prefer this method of determining the spur-to-spur gear dimension to Husting's.

 

I don't know why Gene Husting didn't just use this formula in his article.  The same goes for the mystery surrounding making gear ratio changes for his car:  

 

"Also, as you've mentioned, you can use any combination of spur and pinion with the same total tooth count in that same spacing. A 10T and 50T will have the same center distance as a 30T and 30T."  (Rick Thigpen)

 

This gearing principle should should also have been in Gene's article.

[Alan Draht]

Alan my dragster has run 1.28 geared 28/67 with a 6 volt modified ram motor at 3 to 1 the car did 1.5s.
The cars react differently on 16 v compared to 36 v my car with the 3 to 1 ran 1.17 on 30 volt.
Hope that is a help.

 

Hi Tom,

 

Thanks for that information!  That is helpful.  It's helping me to see that I need to stick with first principles and not overthink this.  

[Alan Draht]

Those gear guards were needed because we ran the cars into bunched up parachutes to slow them down. After a run it would still take some time to cut the silk out of the gears.  

 

Hi Fred,  I assume silk is still used today and that the gear guard is no less necessary.  Anyhow, it's a cool feature of the car and must be replicated!   Besides, I have never machined a part like that and I'm looking forward to it, for both cars.   

[Alan Draht]

I have a 69T Weldun set screw spur gear that you are welcome to Alan.

 

Wow!  Rick, that's great!  I'll PM you.

 

If I can find one more 69 tooth Weldun set screw spur gear I will be able to to the proceed with machining both sets of chassis frame side rails.

 

I want to keep things simple and adhere to Husting's gearing system for both cars.

 

What I think I've learned/ deduced from this exercise is that using the 69T / 23T spur-to-spur gear dimension of 0.7265 inches, Gene Husting's gearing ranges from 70T / 22T to 67T / 25T, and maybe a 66T / 26T.  Gene's article doesn't explicitly state this; you have to figure this out for yourself from clues.

[MSwiss]

Alan,
I'm not envisioning a crumbled up, silk parachute at the end of my strip.

Fred,
Any idea how long of a shutdown you guys typically encountered?

Mine is about 44 1/2 feet.

[Alan Draht]

"If I can find one more 69 tooth Weldun set screw spur gear I will be able to to the proceed with machining both sets of chassis frame side rails."  (Alan D.)

 

Actually, I will still proceed with machining the Husting dragster's mag rails with just one 69T Weldun gear, but I will still need another 69 tooth gear to build the Maldonado dragster.  I will also need two each of the 68T and 67T gears for both cars. I have a couple of 66T gears.

 

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Pablo,  Thanks for your offer!      Pinions are not a problem, however.  It's true that I don't have any 26T pinions, but I may not need to go to a 2.54 : 1 ratio.  I'll think about that some more ...

[Alan Draht]

So what I'm I'm thinking is this:  I can fabricate my own aluminum set screw spur gears.

 

Over the past 24 hours I've been thinking about this gearing problem and I realized that I covered this ground before, years ago when I conceived of the idea of building these dragsters, but my plan was to first build my modernized version of Howie's car, then the dragsters.

 

Nevertheless, when I went looking for vintage parts and raw materials to build my version of Howie's car in 2012 - 2013, I also hunted parts for the dragster projects.

 

Until yesterday I forgot how deeply I had delved into the matter of finding the 70T - 66T Weldun set screw spur gears that I needed for both projects.

 

Yesterday, as I was digging through a drawer containing machine tool stuff -- end mills, drill bits, machine tool accessories, etc., etc. -- I came across a cache of raw materials I have stockpiled for future projects, including a large aluminum round bar, and I thought to myself, "What was I thinking when I bought this?!  What am I going to use this for?"  

[Alan Draht]

Then it hit me.  Years ago I had formulated a plan to fabricate my own aluminum 64 pitch set screw spur gears for the dragster projects, because at that time, same as now, I couldn't find all of the Weldun gear sizes I needed.  So, I purchased the round aluminum bar stock for that purpose.

 

I had also done the research necessary to understand how I would machine that round aluminum bar stock into the spur gear sizes I needed.

 

In one of my machining handbooks, in the chapter on fabricating gears, I came across an equation for determining the outside diameter of a gear based on its pitch and the number of teeth desired.

 

Using the 64 pitch 70T gear as an example, the formula is:   (70 + 2) / 64 = OD = 1.1250 inches.

 

Since 70T was the largest spur gear that I needed to make, round aluminum bar stock would need to be at least 1.1250 inches in diameter.

 

Of course, gears sizes less than 70T with smaller diameters can be fabricated from the same piece of round bar stock after reducing its 1.1250 inch diameter to the correct size on the lathe.

[Alan Draht]

I measured both the 70T gear and the round bar stock.  Both measured 1.1250 inches in diameter.

 

 

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[Alan Draht]

On sale five years ago , I also acquired one of Sherline's programmable CNC-controlled rotary tables and a right-angle attachment to mount the rotary table horizontally onto the milling machine's X-Y table, so that the workpiece rotates under CNC control below the vertical headstock's gear cutter.

 

What stopped me in my tracks from pursuing this any further was the fact that I couldn't find a full set of involute gear-cutting tools needed to cut 64 pitch spur gears for an affordable price seven or eight years ago.

 

Yesterday, I went online and found a complete set of eight 64 pitch, 20 degree pressure angle, involute gear cutters for a reasonable cost.  I ordered a set which should arrive later this week or next.

 

Now I will be able to fabricate the aluminum axle spur gears I need to fill the "gaps" in the 70T - 66T series required to build and race replicas of Gene Husting's and Manual Maldonado's dragsters.

 

Naturally, the fewer aluminum spur gears I need to fabricate the better.  So, I don't need to fabricate 70T gears because I already have two of them, one for each dragster.

 

If I obatin one 69T Weldun gear from Rick T. and can't find any others, I'll have to make another one myself for the second car. 

 

The same holds true for the single 68T Weldun gear available from Don S.:  I'll need to fabricate a duplicate 68T gear.  No 67T Weldun gears have turned up yet, so I will need to fabricate two of them.

 

I don't have any Weldun 26T steel pinions to pair with the 66T gears I have, but that's where my gear-fabrication ambitions end.  There's no way I'm going to try replicating Weldun's steel pinion gears!  

 

Well, I've pretty much thrashed this subject to death...      

[dc-65x]

Hi Alan,

 

I will be happy to send you a 69T gear but it looks like you'd like to have a pair of several different gear sets. Below is a link to EJ's Hobbies website. I didn't see Weldun gears listed there but I've scanned his catalog's Weldun gear selection and he shows everything you need. Now I haven't ordered from him in a few years so I don't know what his current situation is.....you'd have to call him.

 

 EJ's Hobbies website

 

Here are the catalog pages:

 

 

 

Here is a spur gear formula chart:

 

[Alan Draht]

Shouldn't the excellent Magwinder portion of this thread be spun off into a separate thread, so people could find it easier.

 

Cheers

 

Definitely.  I have been setting the stage for launching a new magwinder thread.  The magwinder gearing discussion was the last piece of that process.  The feedback I've received has been extremely helpful.  The new thread would have gotten off to a shakier start without it.  

[Alan Draht]

Hi Alan,

 

I will be happy to send you a 69T gear but it looks like you'd like to have a pair of several different gear sets. Below is a link to EJ's Hobbies website. I didn't see Weldun gears listed there but I've scanned his catalog's Weldun gear selection and he shows everything you need. Now I haven't ordered from him in a few years so I don't know what his current situation is.....you'd have to call him.

 

 EJ's Hobbies website

 

Here are the catalog pages:

 

ej 2 001.jpg

 

ej 1 001.jpg

 

Here is a spur gear formula chart:

 

Gear Chart0001 (2).jpg

 

 

Thanks, Rick!  Like you I visited EJ's Hobbies website as soon as Don Siegel suggested it a few days ago and didn't find Weldun gears there, but I did not look at his catalogue.  Thanks for posting the catalogue pages and highlighting the Weldun gears I'm looking for.  I will call him now.

[Howie Ursaner]

Here's my Magwinder that i built on the tiny table in the corner of my little bedroom i shared with my brother in Forest Hills. I built all my cars in the 60's there. I drilled tiny holes and used a jewlers saw. I made it a little too light and it cracked a rail. It used to have an aluminum body that covered the top. Car is in the LASCM now