Steam Engine Mistake Repair

[macardoso]

Hi All,

I've been working on a PM #6 engine for a buddy for a while now and I just made a big screw up. The frame has a bolt hole circle but the holes are not evenly distributed. I misread the print and drilled them evenly distributed. I need to redrill the holes in the correct spot, but the correct location overlaps the drilled location by about 50%





My current repair plan was to turn some cast iron pins (just bought cast iron bar stock) that are on size with the hole and press them in with some Loctite green bearing retaining compound. I'd then let it cure and drill the holes in the correct position, machining some of the base metal and some of the new pin. These are clearance holes so the loads should be low. When I'm done, I'll either machine or sand the face flat with the hope that the new pins are nearly invisible.

Does this sound reasonable. I'm planning on turning the pins onsize with the hole for a light press rather than risking cracking the casting with a tight press fit. The holes were drilled 7/32 with a twist drill so I'll have to play with the fit to get it right. Two of the holes are 1.5" deep so that is not going to be the most fun to press a pin into.

-Mike

 

[Liljoebrshooter]

I would thread them and the holes. They would never move.

Joe

 

[tq60]

Has the mating part been made yet?

Make same "mistake" on it and call it a day...

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[macardoso]

Has the mating part been made yet?

Make same "mistake" on it and call it a day...

Sent from my SAMSUNG-SM-G930A using Tapatalk

Unfortunately Yes, and on top of that the holes were wonky like this because the bolt heads needed to clear features on the back side of this casting which they do not right now.

 

[macardoso]

I would thread them and the holes. They would never move.

Joe

Not a bad idea. Could tap 1/4-20. I'm uneasy about making my mistake bigger for some reason. Would you be concerned with the pin idea moving? I've never seen that bearing retaining compound come loose.

 

[Moderatemixed]

Good morning. I’m new to this, working on my first engine (a Stuart 10V). The holes are to be spaced differently, per the drawings, but can you see why. Perhaps only one needs to be moved. Or could you just drill the cap to match and call it a modification? I am asking, not because I have lots of experience to offer but rather because I don’t know, but it seems that you are about to go to a great deal of work and potentially going to ruin the casting. I just don’t see the “reason” for the different spacing that warrants all the extra work, and too especially because there is still likely tapping to do, and with pins, and differing cast iron that might be a disaster in and of itself. My thought is to take a page from the rules of golf, “play it as it lies”.

Good luck, but for those of us following you on the path please keep us appraised of what you decide to do.

Derek.


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[TomS]

If you are going to remove 50% of the plug when drilling the holes in the proper location you run the risk of the remainder of the plug falling out. My suggestion is oversize the existing holes so that when you relocate the holes you have a full circle cylinder/plug. As suggested above drilling and tapping is a good idea as is using Loctite.

 

[middle.road]

That's an understandable mistake. Holes are very close at first glance.
Poor drawing style. Should have been shown using coordinate dimensions and not a bolt circle.
With perhaps a note to 'Match Machine' with 'Inboard Head'.
I'm leaning towards threaded plugs + LocTite. You'll be cutting through almost 50% of the plug. 1/4-20 would give the plug a bit more meat.

 

[macardoso]

That's an understandable mistake. Holes are very close at first glance.
Poor drawing style. Should have been shown using coordinate dimensions and not a bolt circle.
With perhaps a note to 'Match Machine' with 'Inboard Head'.
I'm leaning towards threaded plugs + LocTite. You'll be cutting through almost 50% of the plug. 1/4-20 would give the plug a bit more meat.

They are close. I almost screwed it up on the other parts too! I agree with the drawing being a poor style. If I see the abbreviation "B.C." then I automatically assume evenly distributed. Probably not the best thing to do.

Ugh fine... I really don's want to drill or tap the screwed up holes, but you guys are convincing me. Probably tap 1/4-20 and run a die over the cast iron "pins" to turn them into studs. Would make setting the depth easier too rather than press fitting them.

 

[Twirpunky]

Use an end mill to cut the new holes cutting straight down like you would with a drill bit. A drill bit will bend to the side and make a tapered hole to one side. Leave it like it is and put a washer under the head of the bolt. No one will see it once it is put together and for a small model, strength is not a concern. You could even part off some brass washers that will cover the over size double holes. A little extra brass could dress it up the looks.

Good luck.

D