Zee Needs Popcorn

[zeeprogrammer]

Thanks. Material was 303 stainless.

On one end I threaded 3/8" with a 4-40 with no issues but the diameter was smaller than the spec'd OD of 0.112. I was targetting 0.110 but it could have been a couple thou smaller.

[mklotz]

My thoughts, FWIW, on threading with a die...

Stock at nominal thread size*
Healthy chamfer on leading edge of stock
Die opened if adjustable
Ensure that starting side of die (with noticeable lead-in chamfer) is facing stock
Die must be kept square to stock.  Use the front of the TS barrel to guide the die stock when starting
*If still having difficulty, remove ~0.005" from stock diameter
Use plenty of cutting oil (I prefer the smelly sulfurated stuff)
Back off every half turn to break/clear chips.

Incidentally, LMS has an interactive chart for this...

https://littlemachineshop.com/mobile/die_threading.php

For those of you who aren't afraid of a little arithmetic, their chart says...

"Die Blank Size is the Major Diameter less 10% of the Pitch.
This is about the same as common bolts."

which is a lot easier to use than going to their website whenever you want to thread a rod.

[zeeprogrammer]

Thanks Marv!

[zeeprogrammer]

A couple of more parts - the Piston Rod Gland Nut and the Valve Rod Gland Nut.

Rounding the hex didn't go as well as hoped. It doesn't take much to be off. But I'm okay with them.

1st pic are the nuts.
2nd pic shows my setup for knocking off the corners. I'd taken a bit of rod, tapped it, and used it as a holder for the nut.

  If there's a better way, or some hints to be more accurate, let me know.
I'd also be interested in knowing what you do to finish/polish the sides of the hex.

The worry now is whether the rods will fit. My reamers seem to be slightly undersized. 

[mklotz]

My reamers seem to be slightly undersized.

If you don't have them already, consider getting a set of "over and under" reamers.  You'll thank yourself for doing so down the line.

You can make an undersized reamer cut a smidgen bigger by putting a splinter in one of the reamer flutes.  On the rare occasions where I've tried this, I use splinters split from bamboo toothpicks (the kind they stick in your overpriced hamburger at fancy restaurants).  I prefer to use the O/U reamers whenever I can.

https://littlemachineshop.com/products/product_view.php?view=classic&ProductID=3066

[zeeprogrammer]

Thanks Marv. I do have a set. Rarely used.

How does one know when to use an undersized or oversized reamer?
I can see how an oversize might be used after a nominal (or undersized) but you'd have to start with an undersized.

I suspect part of the answer is more accurate (and expensive) measuring tools. 

[b.lindsey]

Zee, I have used undersized reamers probably more than the oversize ones....like for a press fit for a dowel pin or similar applications.

Bill

[10KPete]

Thanks Marv. I do have a set. Rarely used.

How does one know when to use an undersized or oversized reamer?
I can see how an oversize might be used after a nominal (or undersized) but you'd have to start with an undersized.

I suspect part of the answer is more accurate (and expensive) measuring tools. 

Zee, do you have a decent 1" micrometer that reads 10ths on the barrel? Properly calibrated micrometers are essential for making parts to size and especially for reamers. Like any cutting tool there are tolerances and those can be measured before you use the reamer.

On-size reamers are hard because of those tolerances. Where a reamer might cut on size for one material it might cut a half 10th larger or smaller which can upset your plans for a certain fit.

I like to have on-size, a 10th under, a 10th over and one thou over. I think I only have that line up for three or four sizes because I just couldn't get the required fit any other way.

I'm talking about sizes 3/8" and under.....

A hand full of dowel pins, which also come in on, under and over sizes, are really handy for gaging holes and, with that calibrated micrometer, can get you right on.

Those gland nuts look great to my eyes.

Pete

[zeeprogrammer]

Thanks Bill. Press fits hadn't occurred to me.

Yes Pete. I have a "decent" 1" micrometer. I got it many years ago for measuring electronic component leads.
Good to know that different materials can give different results. That may explain a few things I've noticed.

I'm not sure I understand a 10th under/over. +/-0.1 ? That seems awfully big.

[propforward]

Thanks Bill. Press fits hadn't occurred to me.

Yes Pete. I have a "decent" 1" micrometer. I got it many years ago for measuring electronic component leads.
Good to know that different materials can give different results. That may explain a few things I've noticed.

I'm not sure I understand a 10th under/over. +/-0.1 ? That seems awfully big.

A tenth means 0.0001" (tenth of a thou)

[10KPete]

Zee,

Actually, the feel you have developed in using the mic is just as important as the mic itself. You probably know this from measuring small copper wires. It's tough to measure soft, small, stuff! Without extreme measuring equipment, getting nice fits involves much patience and repeated measurement to see if the number you are getting are consistant.

Anyway, I'm very much enjoying your progress and very happy to see you overcoming difficulties to get 'er done.

 

Pete

[zeeprogrammer]

Thanks Stuart. Wow. A tenth of a thou! Can I ever get there? Up to now I happy dance when I'm within a thou.
Thanks Pete. Yes. Reminds me to practice some more on a gauge block I have. (If I can believe the gauge block.)

Some more progress today...and the usual 'crap moment'.

Worked on the cylinder covers. This is the 2nd go. The 1st time I'd used an index cutter to turn the bit that goes into the cylinder. But that left a fairly round edge.
This time I used a 1/8" parting tool.

1st pic shows the beginning of the process. Faced and drilled the holes for the mounting bolts through enough material to make both covers.
2nd pic shows the finished covers. What you don't see is the back of the rear cylinder cover.
I thought I'd be 'cool' and trepan a little detail. Why not? It's a cover. No hole in the center.
But I'd forgotten about the mounting bolts and made the detail a bit large. The nuts for the bolts will overlap.

If the engine runs, and/or I'm a happy camper when done, then I can go back and improve (I mean remake) some of the parts.

I figured some one (Bill?) was getting ready to poke me about a family shot.

3rd pic is what I have so far. Some parts not quite finished.

There's a second set of poorer quality in some corner of the shop. 

  I can't believe it! I left out the crosshead guide! Argh.

[Brian Rupnow]

When I am tapping or external threading, I always back the tap or die off. I go one full turn ahead, back off half a turn, then another full turn ahead, then back off 1/2 a turn. You can feel it when the chip breaks off as you are backing up that 1/2 turn.Use lots of cutting oil, and go slowly. Remember--we're not in a production shop here. Sometimes I have issues getting the die to "take hold" and cut threads. A slight taper on the end of the piece you are threading really helps.---Brian

[crueby]

I can't believe it! I left out the crosshead guide! Argh.

Did you really look for it? Sure the shop gnomes didn't run off with it since you wouldn't give them any of my recipe cookies?!   

[propforward]

Those are some pretty parts. The two parts next to the penny are shiny and look super. Good stuff going on here, this will be a very nice engine.