Turing-Welchman Bombe physical build – part 6.

August 11th, 2015

Right, pressing on here since I have cars I should be building so need this thing done! The other night I started making the covers. Well, the top and bottom ones. I will need to get more steel for the sides and back. On the top of the housing I brazed on a metal strap to which the handle can attach rather than just bolting through the flimsy sheet steel top.


The top and base are simple steel squares drilled for screws that go into tapped holes in the frame. One little rant here. My cordless drill is pretty good except for one silly feature. It has an LED light on it but the light is totally useless! Whatever you are drilling is always in the shadow of the chuck! I think that’s what happens when you let marketing people come up with features, not engineers!

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To mount the castors I positioned them inside the base so I was sure they cleared the frame and marked where to drill the holes. I only had some 3/16ths bolts to attach them at that point and they were a little big. Another problem is the base of the fixed wheels isn’t flat! So the bolts sat at weird angles. I sorted that out today.

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That was about all I got done last night. It was cold then all of a sudden it got very noisy in the garage as it started hailing! It was like someone dropping ball bearings on the roof. I came in soon afterwards!


Today, after an interesting meeting at work, I decided to go out for a drive for some fresh (and chilly) air. It was a nice day so I took the MG out and went and bought some new nuts and bolts for the wheels as well as hinges and a catch for the base. I also got the handle. When I got home I found my new slotted screws had arrived from RS. Earlier my boost converter had also arrived.

Tonight I mounted the wheels properly. The screws I got were too long.


It wouldn’t hurt anything leaving them like that but it looks rubbish so I cut them all down. I have a trick for doing this. I take a steel plate of the approximate length I want for the screws and drill and tap a hole thought it to take the screws. If the plate isn’t quite thick enough you can adjust the length with washers under the screw head. Tighten the screw through the plate then chop off the extra thread with a hacksaw. Then sand the cut off part, while still in the plate, on the linisher.

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The screws will all end up the same length and when you remove it from the plate it also cleans up the cut end of the thread nicely. Things look much nicer without extra, unnecessary threads everywhere.

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Since my correct slotted cheese head screws arrived I did the final mounting of the motors and the main board to the front plate. First I had to  open up the holes the motor shafts fitted through. This is because the motors have a stepped boss in the middle of them. I needed to open the hole up so this boss would fit into the plate and the motor mounting face was hard up against the face plate. I opened up the holed with a hand reamer then finished them off with a sanding drum in the Dremel.

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The motors were mounted with the correct screws and washers and they are held in with Loctite. I also mounted the main board to the back of the faceplate and wired in the motors. I temporarily reassembled things with the correct screws to make sure it all fits. I also powered up the board to make sure it still worked (which it did).

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Pint glass for scale!

I still need to mount the USB hub and work out the battery. I tried a 12 volt 4Ah SLA battery which will fit. The one I have says it can’t be tilted (which seems odd) so I will get another that I can mount on it’s side in the base. I’ll order than from RS. I’ll make a clamp to hold it down to the base. The USB hub I might mount with some double sided foam tape which should be more than enough to hold it. The little boost converter will mount to the main board.

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Tomorrow I will make the housing for the LCD that goes on the left hand side to represent the relay unit. Here is how it looks now with the (unfinished) drums in place.


Whiskey glass for scale!

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