And Now for the Twin

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Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Thu Jan 17, 2019 12:05 pm

Dick, I'm not expecting great distortion from the welding (famous last words), but I've got someone primed to give it a wizz over with a surface grinder afterwards, It's well thick enough (12mm) to stand some loss.
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Re: And Now for the Twin

Post by RGSP » Thu Jan 17, 2019 1:34 pm

That sounds pragmatic. How much a piece of steel is going to distort with welding ought to be predictable, and to an extent it indeed is, but you never know how big are built-in non-uniformities and stresses in your steel plate. My experience with "S" graded structural steel suggests that it's pretty awful for uniformity, but I dare say you're using something a bit better than that, even if you don't know its provenance exactly.
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Re: And Now for the Twin

Post by Mike Rometer » Thu Jan 17, 2019 2:35 pm

That was largely my reason for removing the bulk first, rather than after the weld, that and it doesn't fit the miller easily with the side angles on, and hence the need for farming out the skim.
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Re: And Now for the Twin

Post by Mike Rometer » Sun Jan 27, 2019 5:36 pm

Progress has been a bit piecemeal. The weld preps are done but as I have to weld in the yard it's been delayed by the weather.

The base angles : -
Base-Plate (8) (600 x 450).jpg
Base-Plate (8) (600 x 450).jpg (69 KiB) Viewed 2918 times
And the main plate : -
Base-Plate (11) (600 x 450).jpg
Base-Plate (11) (600 x 450).jpg (68.11 KiB) Viewed 2918 times
Both preps are approx the same size with the one on the angle taking about 2/3 of the thickness (1/4"). Keeping the remaining plate thin assists with penetration. It is probably thinner than would be left for 'stick'.
Base-Plate (9) (600 x 450).jpg
Base-Plate (9) (600 x 450).jpg (56.8 KiB) Viewed 2918 times
For the final set-up a gap of approx the wire thickness will be left also to aid penetration. I'll show that later.
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Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Sun Jan 27, 2019 5:40 pm

So, unable to weld, I had to do something, so I got on with a left-over job, the bottom cylinder covers.

Cyl Cover (21) (600 x 450).jpg
Cyl Cover (21) (600 x 450).jpg (62.96 KiB) Viewed 2917 times
Lots of metal to remove as these are C.I slugs rather than castings, for the same reason as the valve chests (cost and hassle).

Cyl Cover (22) (600 x 450).jpg
Cyl Cover (22) (600 x 450).jpg (57.46 KiB) Viewed 2917 times
Retirement is about doing what floats your boat!

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Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Sat Sep 14, 2019 8:06 am

Whilst to some it might seem I have been idle, it's really only at posting progress on here. I have now more or less completed the base-plate, some minor details changed along the way but nothing significant.

Having prepped all the plates for welding, the weather held things off for a bit, as I have to weld outside and MiG has no friend in the wind. Trying to weld between gusts is just that, 'trying'. First the set-up.

Base-Plate (12) (600 x 450).jpg
Base-Plate (12) (600 x 450).jpg (84.02 KiB) Viewed 2576 times

(Note the pieces of wire in the joints to give a penetration gap.) This set-up was a possible cause of extra distortion that I hadn't allowed for. Hindsight is a wonderful thing! I should have taken a cleaning cut across the under-sides of the side angles AND the set-up bars. I finished up with a slight twist (a few thou) to the final assembly which I surmise could be due to that, as I was careful with the weld order to eliminate that as much as possible. No matter, it all came right in the end.
Base-Plate (14) (600 x 450).jpg
Base-Plate (14) (600 x 450).jpg (71.52 KiB) Viewed 2576 times

Tacking is the first point where distortion can begin. I only used four tacks initially. Right then left, turn the job around then left then right, trying to keep the cooling time constant (contraction). Next was short root runs into the preps.
Base-Plate (15) (600 x 450).jpg
Base-Plate (15) (600 x 450).jpg (69.18 KiB) Viewed 2576 times

DO NOT attempt a complete run down one side, the heat build up WILL build in distortion. Do similar to this the other end, on each side, then do a third in the middle.
Last edited by Mike Rometer on Sat Sep 14, 2019 8:47 am, edited 1 time in total.
Retirement is about doing what floats your boat!

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Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Sat Sep 14, 2019 8:20 am

Oops! Ran out of photo space. :lol:

Base-Plate (16) (600 x 450).jpg
Base-Plate (16) (600 x 450).jpg (81.28 KiB) Viewed 2575 times

Then add more shortish runs in between the others, making sure to work in order so the heat doesn't build in one area.

At this point I did get a bit idle - with the camera! I got engrossed and forgot to take enough pics.

The welds were initially cleaned off with an angle grinder (welder's friend) and also some preps added for the end plates.

Base-Plate (19) (600 x 450).jpg
Base-Plate (19) (600 x 450).jpg (65.98 KiB) Viewed 2575 times
Base-Plate (21) (600 x 450).jpg
Base-Plate (21) (600 x 450).jpg (72.79 KiB) Viewed 2575 times
Last edited by Mike Rometer on Sat Sep 14, 2019 8:47 am, edited 1 time in total.
Retirement is about doing what floats your boat!

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Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Sat Sep 14, 2019 8:32 am

Until recently I have been limited to CO2 for MiG gas so splatter can get quite heavy. A lot will just chisel off or the angle grinder get rid. Obviously the end plates add stiffness, so I decided to add a little more with some gussets one on the inside and two on the outside (each side).

Base-Plate (25) (600 x 450).jpg
Base-Plate (25) (600 x 450).jpg (42.28 KiB) Viewed 2575 times

The assembly was then checked with a straight edge for distortion and found slightly wanting, showing a small twist, as I said previously, I endeavoured to remove that in the press, fairly successfully. I then set up on the mill with shim packing, checking for the best set-up with the D.T.I. and proceeded to true the bottom faces.
Base-Plate (27) (600 x 450).jpg
Base-Plate (27) (600 x 450).jpg (68.23 KiB) Viewed 2575 times

As mentioned earlier my mill is too small for a one hit set-up so a two cut job was called for, checking for the best start with again the D.T.I.
Base-Plate (29) (600 x 450).jpg
Base-Plate (29) (600 x 450).jpg (74.25 KiB) Viewed 2575 times
Last edited by Mike Rometer on Sat Sep 14, 2019 8:45 am, edited 1 time in total.
Retirement is about doing what floats your boat!

A BODGE : - A Bit Of Damn Good Engineering.
Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Sat Sep 14, 2019 8:42 am

It took two passes, as unfortunately on turning the assembly round for the second end, a bit of unnoticed swarf got under one corner and caused a tilt. I never actually found it, but it had to be, as the discrepancy was 0.005" and I was taking 5 thou cuts. The under-side of crank bearing pads were then cleaned off with a long series cutter ( to get in), and the the bearings bolted in and tested. Nothing is ever perfect but these are as close as I ever expected to achieve, perfect! The outer gussets and base corners were shaped with the welder's friend.

Base-Plate (30) (600 x 450).jpg
Base-Plate (30) (600 x 450).jpg (65.84 KiB) Viewed 2574 times
Base-Plate (31) (600 x 450).jpg
Base-Plate (31) (600 x 450).jpg (66.12 KiB) Viewed 2574 times

Now I need to look at the crank webs again, or the con-rods, or???
Retirement is about doing what floats your boat!

A BODGE : - A Bit Of Damn Good Engineering.
RGSP
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Re: And Now for the Twin

Post by RGSP » Sat Sep 14, 2019 2:16 pm

Now you've got all those stresses to either get rid of or live with.

I recommend marinading the welded unit in something which will produce a thin organic film on the steel, having dissolved a bit of grease beforehand.

Something around a 4% v/v solution of methanol in pure water would do. If need be though you can use ethanol, and the water can be a bit brown too.

In fact, it often works better for the machinist to just drink the marinading solution, leaving the welds alone. Nett stress is enormously reduced.
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