This is the drawing from the parts book that was used to dimension the transmission. Measurements were also taken from the prototype in Queensland.
The transmission started out as a piece of 65mm pipe, 5mm wall thickness. It was cut to length (240mm) and carefully quartered on a large bandsaw.
Here I am in my friend Bob Waterford's workshop making the final cut.
Here are the two quarters of pipe separated by a piece of 6mm plate 240x50mm. This was welded together to form the base of the transmission. The remainder of the transmission was fabricated in a similar way.
This photo has been posted previously and shows the fabrication of the transmission complete.
The fabricated transmission was placed on a surface plate upside down to mark out the bearing centres. It was then clamped to the mill table and the holes bored.
The fabricated transmission was placed on a surface plate upside down to mark out the bearing centres. It was then clamped to the mill table and the holes bored.
Lindsay:
ReplyDeleteI'm interested in how you established the bores and faces of the transmission. I've just completed welding the main "box" and I'll be starting on the brackets at the rear of the transmission soon. These will be silver brazed to the box.
When it comes to machining it seems to me that the bores for the rear axle are critical to establishing the geometry of all the other bores and faces. Did you begin with the rear axle bores and then machine side faces and final drive pinion bores relative to it? Then work round to the gearbox bores and faces?
I expect to do most of the machine work with the transmission upside down on the machined flanges for the top covers.
By the way, I like your gear hobbing set up. Not having any CNC at my disposal I'm limited to conventional gearcutting with dividing head and Brown and Sharpe style cutters.
Regards,
Alan Suttie
Alan
ReplyDeleteI started with the steering clutch shaft which also sets the position of bevel pinion and gear cluster.I then used the ratios 25-48,28-45,32-41.
This gave me the position of input shaft which is
also the height of the power take off
I adjusted the ratios in the final reduction to fit in the scale housing,(30-73)1.5 module.I adjusted the mesh using epoxy .
You will note that I have not followed the prototype.I am not confident that I can make the engine run at 650 rpm
Alan I would be happy for you to telephone me
My phone no. is 02 62887752
Regards
Lindsay Drabsch
Lindsay:
ReplyDeleteI'd be happy to call you, perhaps tomorrow, Thursday here and obviously Friday there. I'll give it a try at 4:00 pm here, that's 10:00 am there by my reckoning, neither an antisocial time.
I've also been intending to work in significantly more mechanical reductions since the smaller engine will probably turn twice the rpm of the full size. I've worked out a number of cases at engine crank speeds from 1,000 rpm to 1,500 rpm to give me a nice slow forward speed of approximately .3 feet per second in low ratio.
I'd had similar problems in my two previous IC engined models with scale forward speeds. My Aveling DX road roller (loosely based on Edgar T Westbury's design) used the prototype's gearbox and twin clutches, not the friction drive.
My second IC attempt (also loosely based on an ETW design) was a diesel mechanical locomotive - running on gasoline. In this model I used a later design of transmission based on Gerog Constantinesco's infinitely variable harmonic transmission.
The crawler tractor will be a nice companion for the roller since it's the same scale of 1 1/2" to the foot.
I've modelled the entire tractor drive system in Excel so I can look at the effect of different numbers of teeth etc. As in my previous two models once I'm happy with the result I'll add some gear cutting info and work out blank diameters etc.
Spent some time today on the rear axle brackets, they get progressively difficult to hold as each machine operation is completed. I won't make the hole for the rear axle yet, that can wait until I have the transmission upside down on the mill table and make the semicircular rough bores with a ball end mill.
Regards,
Alan Suttie