Monitor Steam Engine

[Jasonb]

Why not just forget all the holes you have in the cylinder, rotate the end covers 30degrees and drill new sets of six holes at each end which will fall betwen the dodgey ones.

If you use the existing cover holes to spot through to the cylinder even if the cover holes are off you will still get them all to line up as long as you mark the orientation of the covers.

[zeeprogrammer]

Woke up this morning with the very thought Jason has.
Simple. And I've got the covers to set/doublecheck the hole placement.
Thanks!

Thanks Geoff. Had it been one hole that was wrong I would have gone that way.

First job is to try and find out what went wrong.
I know the biggest reason for the bad end was the sticky tape and lapse in verifying position.
Need to find out why all the holes are on a larger diameter than the ones in the cover.

For that matter...which one is right. I'll check that first.
Had I moved the table between cylinders and covers...that would explain it too.

[zeeprogrammer]

I checked the mill with a square and bearing shaft. Moved the head up and down.
Not that it's perfect...but not nearly the error I'm seeing in the holes.

Further inspection shows I was wrong about the diameter of the placement of the cylinder holes being larger than the covers.
Half are spot on, or nearly, the other half moves out.
That tells me the cylinder was tilted.
Looks like about .02" or slightly more. If there were swarf or something under the cylinder...that may explain some of the problem. I tried to be careful about that so I'm thinking it may be more of a problem of clamping.

I'm not looking further into it. That is, I'm not going to calculate how much had to be under the cylinder to tilt it enough to have that error 2" inches away.

I checked both cylinders with the covers on both ends that take the piston rod and put a long rod through. One is slightly more tight than the other...but loose enough to know that a bit of running in (or better rod) will be okay. So the bores still seem fine at this point.

So I'm not in deep poo-poo yet. Not even with T when I nodded off during her game. 

I'll redo the cover holes on the one cylinder. Both ends. I don't think I need trouble with the other cylinder.

Thanks for listening to my blather and for the help!

I had a crap day today and this has picked me up a bit. 

[zeeprogrammer]

Thanks for listening to my blather and for the help!

I mean 'reading' my blather.

And you're doing it again. 

[crueby]

Thanks for listening to my blather and for the help!

I mean 'reading' my blather.

And you're doing it again. 

I ignored the blather, concentrated on the bluster.

[zeeprogrammer]

Bluster? Whose?

Can't be mine. I'd have to have something to bluster about. 

[Pete49]

Loving this thread as much for the blather as the bluster  oh and the metal work 
Pete

[zeeprogrammer]

Thanks Pete.
...and that's no bluster. 

Metal work...sigh. Not on the back burner...but life is getting in the way.
Roof, chimney, gutters, fridge, door, helping the little one move, T...well not so much T. Not that I'll admit.
Everything seems to happen at once. And always at bonus time.
A new mill is in jeopardy. 

The plan...

Marking the cylinder using the covers. Using a transfer punch so I know where the holes should be.
Then drill and tap the one 'bad' cylinder. The other cylinder I'll leave alone.

My indecision is starting to waffle.

New mill or new lathe? Still a few months off.
I know the mill I want. The lathe...I think one of the big things is a collet chuck.

One of the forum members is ignoring me.
Might mean a  upside his head. 

[crueby]

Zee, when you drilled the holes, did you spot drill first to prevent the drill bit from walking a little before biting in? On smaller bits especially it can sdkate to the side. I use a center drill bit first, others use a spot drill (think that is correct term). Starting a small drill with a punched mark in aluminum can be bad since it makes a work hardened spot that can make the bit skate more.

[zeeprogrammer]

when you drilled the holes, did you spot drill first

Yes. I use a center drill bit.
I haven't done the new holes yet. The punch marks are light and just so I can verify that that's where I'm going to center drill and drill.

[PStechPaul]

You probably know this, but you can set a divider so that the points are at the distance of the radius of the 6-hole bolt circle, and then walk it from each hole location to the next to verify that dimensions are correct. This works well if the locations are prick punched or center punched.

Also, make sure the center punch is ground to a 90 degree included angle (or even larger). This will help guide the center drill or spotting drill to the exact center. There is some difference in opinion about the angle of the spotting drill:

http://bbs.homeshopmachinist.net/threads/69380-Spotting-Drill-Lesson-Needed?highlight=spotting+drill

http://bbs.homeshopmachinist.net/threads/69366-drilled-holes-out-of-place?highlight=spotting+drill

One reference calls for the 90 degree spotting drill for regular HSS twist drills, and 135 degrees for carbide. The sharper angle allows the cutting edges to hit the outer diameter of the hole, rather than the chisel point of the drill. The wider angle causes the point of the drill to slide toward the center. So it may depend on how well the drill is sharpened, and if it has a "split point" or other geometry.

I have a spotting drill that can be made from a piece of round HSS or a broken center drill, and it is very stiff so that you don't have to worry about it moving or breaking, as can happen with the point of a center drill:





I also have a longer double-ended spotting drill:



You can see how the point is ground so that there is a well-defined center point and the cutting edges are 90 degrees to it:

[zeeprogrammer]

Thanks Paul.

This brings up a question...

spotting drills vs center drills

(I believe there's been discussion on this before...but well...don't remember.)

My center drills have a tip to them. I see that the spotting drills do not.

What are the thoughts on advantages/disadvantages of both?

[crueby]

Tip angle on spotting drills can be different, as paul mentions. Some people have had the tip on center drills break, I never had that happen, but usually don't drill very deep with it.

[10KPete]

Carl, there are spotting drills and there are combined drill/countersinks which are used to create...... centers! Thus frequently
called......center drills!! 

Couldn't help throw that in.....

Pete

[zeeprogrammer]

I've busted one tip before. And it's a big fear doing it again while working on the cylinders right now.

Pete....argh!