7mm Steph's modern traction workbench

[Steph Dale]

A solution has been found involving a number of components from Branchlines and a stack of ball races. In short we have here enough parts to make a conventional motor/gearbox unit (ball raced) which then has a set of U/Js off the back of the motor driving a second, axle mounted gearbox at the other end of the bogie:



Needless to say it's not quite that straightforward: The gearbox needs tweaking to take the Canon motor in the desired configuration as well as adjusting to take the ball races and some necessary reinforcement. Plus, of course, there's the assembly of the second gearbox.

And having to do the whole lot twice!

Steph

 

[Dog Star]

How much of the motor protrudes into the space of the cooler group?

 

[Steph Dale]

Graham,

I've decided to orientate the motor the same way as the original kit (hence the need to modify the gearbox). In this configuration the motor only just extends into the base of the body and is allowed for in the design of the kit. The dotted blue horizontal line shows the rough height of the floor of the cooler group so I suspect it'd all fit together quite happily even with the motor fitted to the gearbox as supplied. It might be a bit more visible below the bogie though.

Steph

 

[Dog Star]

A cardan shaft between first and third axles with a one stage gear tower for a cardan shaft to the motor in the fuel tank area seems to be not much more work.... neither shaft would be above floor /below bogie solebar level.

regards, Graham

 

[Steph Dale]

A cardan shaft between first and third axles with a one stage gear tower for a cardan shaft to the motor in the fuel tank area seems to be not much more work.... neither shaft would be above floor /below bogie solebar level.

regards, Graham

I looked at that - there are problems. First off would be the need to make 6 gearboxes rather than just two. Then getting the prop shaft to run through the body/floor without compromising strength or having to make major alterations to the body; the kit doesn't have (or need!) a separate chassis and builds up as a bathtub, see here: http://www.7mmlocomotives.co.uk/gallery2/main.php?g2_itemId=5479. The large central motor would also get in the way of the speaker chamber.

Steph

 

[Dog Star]

Sometimes Kettles seem easier.

 

[Steph Dale]

Sometimes Kettles seem easier.

That's because they are! I know just what you mean...

 

[Steph Dale]

Progress continues; finished drafting the gearboxes.

Now it's time to frame them up for the etchers, but (with Cynric's chuckle metaphorically in my ears) the hard bit is done...:


Steph

 

[Dog Star]

Nice to see a gearbox with four sides rather than the typical three... apart from adding a top or a bottom plate, how will you keep the sides parallel?

regards, Graham

 

[Yorkshire Dave]

Split axle (version 2 or 3) or American pick up, or a combination of both or wipers on top of the wheel treads hidden by the frames or split frame bogies? Or not got that far yet?

 

[Steph Dale]

Nice to see a gearbox with four sides rather than the typical three... apart from adding a top or a bottom plate, how will you keep the sides parallel?

Graham,
I was intending to put a plate through the middle of the gearbox, but getting clearance around the gears and bearings is tricky. I'm going to see how these go together and decide if I need to make any design changes then.

Split axle (version 2 or 3) or American pick up, or a combination of both or wipers on top of the wheel treads hidden by the frames or split frame bogies? Or not got that far yet?

Dave,
Split axles if possible. I'm still aiming for 12-wheel pick-up, which will probably mean using the type 2 axle break as it's nice and compact. This is part of the reason for the gearboxes being asymmetrical; it leaves a little width on one side for an insulation break. The insulation in the bogies will done using your trick of a copper-clad paxolin washer under each of the bearings.

Steph

 

[Dog Star]

Steph (orDave),

What are version/type 2 and 3 split axles?
What is the insulation trick using copper-paxolin washers?

Intrigued of near-to-Basingstoke

 

[Steph Dale]

Graham,

Dave and I have three approaches to making split axles:
Type 1: A near-conventional approach using two holes cross drilled through axle, with piercing-saw cuts and epoxy to provide the insulation
Type 2: A variation on the above using only one cross drilling and a 'jigsaw puzzle' shaped cut. Slightly trickier than the above, but can be made very compact and is still pretty strong.
Type 3: Drill the length of the axle for 2mm GRP rod, epoxy and then cut around the axle to provide the insulation.
All detailed on my webpages. Or actually not: here are the URLs for the pages that are not yet in the public areas:
http://www.euram-online.co.uk/tips/splitaxle/splitaxle1.htm
http://www.euram-online.co.uk/tips/splitaxle/splitaxle2.htm
http://www.euram-online.co.uk/tips/splitaxle/splitaxle3.htm

About halfway down the second page is a couple of paragraphs (still sadly lacking diagrams) which shows a gearbox modified for use with split axles, as in this picture: http://www.euram-online.co.uk/tips/splitaxle/2splitaxle07.jpg together they show the use of a copper-clad washer to insulate a bearing from a frame.

I hope that helps,

Steph

 

[Dog Star]

Thank you Steph, much clearer. For type 3- use of a 6BA tap to provide a "key" inside the bore of the axle is a neat idea. What is the failure rate, as regards conductivity, in producing axles to type 3?

regards, Graham

 

[Steph Dale]

Graham,

Providing a continuity check is done after the groove is cut and before it's filled you can get them all to pass...
Bright light and/or magnifying glass is optional if you need to find where the groove needs to be made deeper though!

Steph

 

[Dog Star]

Bright light and/or magnifying glass is optional if you need to find where the groove needs to be made deeper though!

"Bright light and/or magnifying glass is optional if you need to find ... the groove" .

 

[Steph Dale]

"Bright light and/or magnifying glass is optional if you need to find ... the groove" .

Hmm; that would seem to apply equally to my preferred sort of turntable...

 

[Steph Dale]

Yesterday's big event, other than a trip to Simon's emporium, was the artwork for the gearboxes being accepted by PPD and the placement of an initial order.

Patience really isn't one of my strong points...

Steph

 

[Steph Dale]

Patience will out...

Frets arrived on Saturday morning, but with a busy weekend already on the cards it wasn't until this evening that I was able to make an attempt on assembly. So from this:


To this:


In about an hour. That's with checking every dimension against the drawings/artwork specs. So I'd expect to get a set together and running in about half that time under normal circumstances.

So time for a quick appraisal, first the good:
The shapes all work - they can be assembled (and quickly).
Etch tolerances have come out on the money.

The bad:
Tolerances quoted on the gears are out by a couple of thou" - redraft required.

Improvements:
Corner reinforcement would be nice*
I'm now aware that there are other smaller Mashima motors with the required 15mm+ motor shaft length*

So the next couple of hours will see the gears re-pitched to allow a couple of thou" running clearance. While I'm at it I'll add some triangular tabs into the corners for reinforcement and I'll add a couple of holes in the motor mounting plate to allow Mashima 14xx and 16xx motors to attach.

Other than that I'm open for comments and advice.

Oh and one way or another, these will be available for sale in a little while.

Steph

 

[mickoo]

Steph,

Those look very nice, how much smaller in dia are the 14xx and 16xx motors, would a 14xx motor be almost fully under floor? The 14xx might suit shunty plank layouts but I suspect you'd need the bigger 18xx for longer trains etc.

Kindest