A Little Machining Problem

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A Little Machining Problem

Post by Carrdo » Tue Jul 16, 2019 5:07 pm

Hi Folks,

As you know, I like to build (Hudson) locomotives but I need your machining expertise.

Does anyone have a practical way of attaching a smokebox shell to a cylinder saddle so that the bolt holes align completely? These holes have to be drilled radially and I have a way of marking and drilling each part separately but I do not like it as there is no margin for error here. Is there any other way of drilling these holes when the parts are clamped together or is there some other fool proof method for carrying out this operation?

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Re: A Little Machining Problem

Post by wewilliams » Tue Jul 16, 2019 6:54 pm

Transfer screw or punch?

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Re: A Little Machining Problem

Post by ALCOSTEAM » Tue Jul 16, 2019 7:03 pm

Can you reach inside the smokebox with a right angle drill and make your holes

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Re: A Little Machining Problem

Post by Fender » Tue Jul 16, 2019 8:49 pm

In historical full-size practice, the holes were laid out on the smokebox and then match-drilled through the cylinders from the inside, using a “spider” frame that held the drill in alignment with the centerline of the smokebox.
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Dan Watson

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Re: A Little Machining Problem

Post by KarlKobel » Tue Jul 16, 2019 10:57 pm

I drilled them radially using the layout from the saddle.
I only had to chase them but there wasn't much material removed,

My Smokebox is split, so it was easier to clamp to the mill table.

http://www.karlkobel.com/unsorted/Smoke ... 45285.html


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Re: A Little Machining Problem

Post by Pontiacguy1 » Wed Jul 17, 2019 6:23 am

I always drilled the saddle first. Then I clamped the saddle and the smoke box together using all thread rod and a couple of pieces of scrap, mounted them in the mill, and then drilled the holes. Make yourself an extension for whatever size bit you are using so that you won't hit the saddle with the drill chuck. In my case, I was using a 1/4" drill, so I used a piece of 1/2" diameter stock, drilled and reamed a 1/4" hole in one end, and then added a setscrew so that the drill bit would be powered. Worked great. Like I said, drilling the saddle first and then using it as the drill template worked great for me. I also have used a piece of channel steel that I bolted down and centered under my spindle, and now I can just sit the saddle down on there, move it back and forth, and rotate it around to align these. Works just the same using a drill press. That's a quick way to drill all those holes for the rivets in a smokebox too.

I've actually drilled them together before. Lay out holes on the smoke box underside, then clamp them together. Use a center drill in the aforementioned extension and drill the pilot hole, then drill through with the tap drill size, then separate them and drill through and finish each indivudual piece.

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Re: A Little Machining Problem

Post by Bill Shields » Wed Jul 17, 2019 8:59 am

I drill the saddle holes using a rotary table to get all 'normal'

Clamp the smokebox to the saddle front and back with machinist's clamps.

Next take a piece of drill rod that is the same size as the drilled holes, put a concentric point on it.

Make it long enough to protrude through the saddle casting and have something hanging out the back.

using a long machinist's clamp, squeeze the 'pointer' into the hole to make a 'center spot' on the smoke box surface.

you can follow from there....
Too many things going on to bother listing them.

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Re: A Little Machining Problem

Post by blff cty lcmtv wrks » Wed Jul 17, 2019 10:58 pm

I used a hand drill with a tap drill for a #8 tap. made it long with an extension. drilled the saddle first. aligned every thing up. clamped it all together. with the same hand drill, i drilled through into the smokebox. tapped said holes. then went back to the saddle and drilled the clearance holes, with a generous amount of wiggle room and bolted it altogether. I have always made my smokeboxes out of a chunk of schedule 40 8 inch pipe. I build my petticoat pipe out of a chunk of bar stock, and press it up into the stack. I had one fall out of the stack and down onto the blast nozzle. needless the boiler acted like crap, and the exhaust sounded like somebody blowing over the top of a coke bottle. sounded funny.

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