Drawing queries

[paul]

I'm in the process of converting an imperial drawing to metric for my next mini engine. Can someone tell me what #2-56 means in the following context?



I assumed it meant two holes using a number 56 drill but the instructions call for 'a solid mounting' and #56 drill is only just over 1mm!

Also the drawing shows P, C and S at various places, each in a circle. Am I right in thinking these stand for 'push', 'clearance' and 'sliding' fits?

Finally, and not related to the drawing per se, the design calls for a cylinder in 'hard aluminium'. I've not seen that before, what is it and could I use some other material (this is for a Scotch yoke engine rather than my usual 'wobbler' type)?

EDIT: #2-56 can't be what I thought as the flywheel has one grub screw with #5-40 before it. Thinking....

[baggo]

The #2-56 is the thread size Paul - No 2 ANC or ANF, outside diameter 0.086". Not sure about the P, C, and S though.

John

[paul]

Thanks John, I just googled #2-56 and found the answer. Doh! Looking at a chart that still looks like only 2mm or so though.... maybe I'll beef it up a bit ;D (plus I haven't got a 2mm tap/die yet!).

Here's a bit with those letters:



The narrower part with 'P' is fitted into a hole in the frame and then loctited so I thought it might be 'push fit'. Why there should be a 'C' and an 'S' on the bearing hole though puzzles me - surely that would require a sliding fit?

Thanks muchly

[circlip]

Paul, go back onto "the site" and ask them, the yanks have their own way of doing things. Think you'll find that "Hard Aluminum" (spelling is OK) is one of the extruded aerospace types- 6082T6
Can't see rest of first drawing but your 19mm could be 20 and your 27 25. 3/4" & 1and1/16"?
When your converting use sensible numbers, 3/8" is 9 or 10, not 9.6, as long as the mating parts fit EACH OTHER it doesn't matter which way you jump, but in the case of the bush you've shown,10 cos the bore is going to be 5 for the shaft that goes through it not 4 or 4.7. I said 20 for above cos it's easier to measure 10 either side of C/L than 9.5?
Just been across "THERE" Paul, you missed the box, Close and Smooth.

[paul]

Close, smooth and push then - ta.

I've converted it all now. Yeah in that case I could've used 20mm instead of 19 but I'm used to thinking 3/4=19 (within a gnat's) when using bar stock

The only bits I'm a little uncertain about are the crank throw/cylinder length&position and the lengths on that bearing as both will be failry critical. I just need to sit and stare at it a while longer

EDIT: Maybe cast iron would suffice instead of a lump of Boeing?

[circlip]

If you want to use cast iron why not, but aerospace grades are not exotics anymore. you can use a lump from a crashed class 465, most of it is made from it, the bodywork anyway. HE30 is hard, HE15 is softer. Check with your normal stock supplier you'll be surprised what's on offer.

[havoc]

Dural would qualify as a hard alu. Indeed the first time I heard alu mentioning for steam engines.

If you need to use loctite, then a push fit is a bit too narrow. Remember you need space for the loctite. I would use a sliding fit h7/H7 and position it during curing so it can center itself. Or you could make it a light push fit and keep the faces a bit rough so the loctite can wick into it.

[simonwass]

havoc said:

If you need to use loctite, then a push fit is a bit too narrow. Remember you need space for the loctite. I would use a sliding fit h7/H7 and position it during curing so it can center itself. Or you could make it a light push fit and keep the faces a bit rough so the loctite can wick into it.

When loctiting always machine the item to a very good fit then machine a 2thou recess leaving a 16th or so full size at each end of the part. This way you still get the loctite gap but have an assembly which runs true.

[Peter W.]

simonwass said:

When loctiting always machine the item to a very good fit then machine a 2thou recess leaving a 16th or so full size at each end of the part. This way you still get the loctite gap but have an assembly which runs true.

Good advice -- somebody called this the 'cotton reel' effect.

[Shawki Shlemon]

Slightly off the subject ,I use similar method when silver soldering good fit items together by putting grooves for solder to flow.just an idea .