Genghis's 7mm Workbench

[Genghis]

Work progresses on the loco frames. No issues so far, but that is mostly thanks to Bob Alderman who provided the supplementary instructions. There are no drawings with the original instructions. Peter Dobson should have produced them but became incapacitated before he finished them.

 

[dibateg]

Interesting to see the O4/8 progress, they are/were a rarity in O gauge for a long time Allen Hammet built a couple a few years ago for me and a friend, by combining an O4/7 kit with a set of DMR B1 etches...



You couldn't get more unglamarous!

Regards
Tony

 

[mickoo]

Presumably acid, somehow etching the zinc out and leaving the copper to give a pink hue?

I've heard that too

 

[Genghis]

Interesting to see the O4/8 progress, they are/were a rarity in O gauge for a long time Allen Hammet built a couple a few years ago for me and a friend, by combining an O4/7 kit with a set of DMR B1 etches...

Hopefully in stock for Guildex!
David

 

[Genghis]

I would usually have ensured that I have a rolling chassis before doing anything else, but I realised that the larger diameter holes in the coupling rods need opening out a fraction so that the head of the bush fits in fully. I've ordered a slot drill so while I wait for that to arrive I have made up the footplate. This would have been the next job anyway as I like to check how the motor gearbox is to be fitted. With that done I will also need to work out where to fit the pick ups as the frames do not have any pre-existing locations marked out. There were lots of rivets to emboss on the main section of the footplate. This is where I am now:

 

[Genghis]

The slot drill arrived so I was able to complete the coupling rods. The bush sits nicely inside the boss.



I decided I wasn't happy with the front footplate, so after wafting the meringue browner at it I was able to rebuild it and add the other parts of the framing that stiffen the footplate assembly.



So back to the frames tomorrow. First to check that the chassis rolls nicely with the rods on and then to add the motor mount and mark out the locations for the pick ups.

 

[simond]

Hi David,

Nice work with the slot drill, and a useful alternative to the process I used with a mini-CNC mill.

do you have any photos of how you held it whilst you machined it?

atb
Simon

 

[Genghis]

Hi David,

Nice work with the slot drill, and a useful alternative to the process I used with a mini-CNC mill.

do you have any photos of how you held it whilst you machined it?

atb
Simon

Not ideal.....



As the holes were nearly there and only needed a smidgeon removal, I could line up easily. I half expected to have to raid the stores for another set of rods but luck was on my side.

 

[spikey faz]

Hi David,

Nice work with the slot drill, and a useful alternative to the process I used with a mini-CNC mill.

do you have any photos of how you held it whilst you machined it?

atb
Simon

I'd be interested to know more about this process as well, please.

Mike

 

[Genghis]

I'd be interested to know more about this process as well, please.

Mike

Really not much to tell. I have a Proxxon milling machine which mostly gets used as a vertical drill. The slot drill was set up in the chuck and the workpiece lined up by eye and feel: gradually moving the stationary drill down until I was confident that it was aligned with the middle of the slot. What I should have done is clamp the coupling rod close to the boss onto the X-Y table and then line it up. As I said above, because the rods already had a near correct diameter hole and a very small amount to machine out, I took the risk of simply holding the workpiece and then switching on the mill at maximum speed. Gently lowered the cutting edge and quickly move it back up again. There was less than 0.5mm to take out but I needed a flat surface which of course you don't get with a normal drill if you don't drill through a piece.

David

 

[simond]

Great respect, sir, you’re a braver man than I, Gunga Din!

 

[Genghis]

Great respect, sir, you’re a braver man than I, Gunga Din!

Picture of fingers taken after the machining! I will not be so stupid next time.

 

[Rob Pulham]

What size slot drill did you buy David?

 

[Ian@StEnochs]

David,

A slot drill is not ideal nor very easy to set up accurately to counterbore an existing hole. For countersinking crank pins I use a spot facing cutter, 5/32" with a pilot, which locates the cutter exactly on the same centre as the existing hole.
I have put a brass bush on the pilot pin which fits the predrilled hole in the rod.
Held in my drill press with the rod held down by hand it needs a light touch and a bit of cutting fluid but leaves both hole and counterbore perfectly concentric.

Ian.

 

[spikey faz]

Up until now I was not aware of the existence of these sort of drills. So thanks for posting the above info.

Mike

 

[Genghis]

What size slot drill did you buy David?

0.157"

Strangely a 4mm one wasn't quoted where I looked (Drill Service).

 

[Rob Pulham]

Thanks David,
I have had to buy imperial sizes from Drill Services to get the 'metric' size that I wanted on occasion too.

 

[Genghis]

David,

A slot drill is not ideal nor very easy to set up accurately to counterbore an existing hole. For countersinking crank pins I use a spot facing cutter, 5/32" with a pilot, which locates the cutter exactly on the same centre as the existing hole.
I have put a brass bush on the pilot pin which fits the predrilled hole in the rod.
Held in my drill press with the rod held down by hand it needs a light touch and a bit of cutting fluid but leaves both hole and counterbore perfectly concentric.

Ian.

I think your solution is better. Fortunately for me the outer laminations of the coupling rods and bosses were already the larger diameter, so alignment was pretty automatic.

David

 

[Genghis]

Bit of a slow day at the bench, but I did manage to fabricate and fit the gearbox torque reaction arm.





Then it was time to try out the coupling rods.




It rolls!!!

 

[Genghis]

Work continues. Pony truck constructed, brakes and sandpipes added. The brake pull rods were all exactly the right length!







The leading brake beam swings up for access to the pony truck pivot.