Machining a backplate - part 3 (or how not to)

SteveM · Post by **SteveM** » Wed Apr 04, 2007 9:12 am

In the previous installment:
http://www.chaski.org/homemachinist/vie ... hp?t=76335

I had finished machining the backplate on the spindle and had marked it off for drilling.

As the quill on my drill press has some slop, I decided to use the mill. I bolted the faceplate to the table up on some parallels and used the following procedure:

Centered the spindle over the marks with a wiggler
Used a center drill to spot drill
Drilled through with the clearance drill
Drilled part way down for the counterbore using a drill
Finished the counterbore with an end mill
(I didn't have a counterbore of the proper size).

After three holes, took it off and put it on the chick to see how I did, and it would not go on.

I COUNTERBORED THE WRONG SIDE!

DOH!

I can't counterbore from the other side, or I would end up with a through hole.

Remembering at this point that the objective is to make parts and not tools, I made some inserts, press fit into the holes with the through hole drilled in them. I'm going to attach the chuck with hex head bolts or socket head cap screws not in counterbores.

The correct solution will be to drill and counterbore new holes in between the old ones, which I will do at some point in the future.

What I should have done while marking it out would have been to take a marker and write across the face:

"COUNTERBORE OTHER SIDE"

Sort of how people getting leg surgery mark the WRONG leg "OPERATE ON OTHER LEG".

The next step will be to make the soft jaw tops. I have two different sizes of aluminum bar stock the proper width. I got the dimensions for the jaw tops from Hardinge's web site. Just need to cut to length, mill two grooves, drill and counterbore (from the correct side) two holes and make a key.

Steve

BadDog · Post by **BadDog** » Wed Apr 04, 2007 11:56 am

Nice work.

And I feel your pain. Sad to say, but I've done similar things on more than one occasion. I keep telling myself to get in the habit of marking things "not this side" and such, and I often do, but then some "simple" thing comes along and I screw it up. <sigh> In fact, funny you mention the soft jaws because that is one place I messed up in a very similar way while cutting the tongue-n-groove.

Good luck and thanks for the update...

kapullen · Post by **kapullen** » Thu Apr 05, 2007 6:18 am

Steve,
Don't feel lonely!
We all have a couple of whoops's out there.
I must have a dumpster full.
Kap

SteveM · Post by **SteveM** » Thu Apr 05, 2007 7:02 am

Someone once said that a good machinist has a pile of scrap under his workbench.

I also like some sayings that Chuck Hackett has posted on his web site (http://whitetrout.net/Chuck/ ):

"Good judgment comes from experience, experience comes from bad judgment"
- Author Unknown

"He who never made a mistake never made anything!"

"Life consists not in holding good cards but in playing those you hold well."
- Josh Billings

"Experience is that marvelous thing that enables you recognize a mistake when you make it again."
- F. P. Jones

Steve

BadDog · Post by **BadDog** » Thu Apr 05, 2007 3:24 pm

SteveM wrote:"Experience is that marvelous thing that enables you recognize a mistake when you make it again."
- F. P. Jones

I particularly like that one.

SteveM · Post by **SteveM** » Thu Apr 05, 2007 8:04 pm

"The only thing we learn from history, is that we don't learn from history"
SteveM (as in me)

Steve

gt2ride · Post by **gt2ride** » Thu Apr 05, 2007 8:54 pm

I make my share of mistakes also. I have started making notes and taking them to the mill or lathe. What do you do to keep from making mistakes?

Post by **Harold_V** » Thu Apr 05, 2007 9:14 pm

gt2ride wrote:I make my share of mistakes also. I have started making notes and taking them to the mill or lathe. What do you do to keep from making mistakes?

As offensive as you, or others, may find this statement, what you do is *become* a machinist. Sorry if it does offend, for it was not intended to.

It takes, literally, years of constant practice to run machines without making mistakes, and even then you're not immune. Fact is, sometimes you're just a lot faster at making them.

You can liken running a machine to playing a musical instrument. Anyone can make it work, but it takes someone with considerable experience (practice) to do the work routinely, with precision, without supervision, in a timely fashion. To assume you can do so without going through the same routine those of us that work in the trade have endured is a real slap in the face to us. I can't speak for others, but I demand respect for my years of experience. I worked hard at mastering my trade.

Please----not only you----but anyone reading these words:

When you consider machining, think of your profession or trade and consider what it took for you to become proficient in what you do, and the hurdles you encountered on your journey to today. Why would anyone short change a machinist, thinking that they, too, share the same skills when they haven't paid the dues?

One of the best exercises you can use is to always work to the dimension, not the tolerance. Try to hold dimensions as close as possible, without polishing unless that's a needed procedure (like fitting a bearing). By so doing, you'll improve your skill level considerably, making it all the easier to hold tight tolerances when necessary. Besides, the extra time you dedicate at first, while learning, provides extra thinking time so you might avoid doing something stupid.

Most importantly, don't get discouraged. My first ten months in the shop (as a trainee, being paid) were horrible. The worst possible thing that could happen did------I lost all confidence in what I was doing. Once lost, it's very hard to recover.

Luck!

Harold

SteveM · Post by **SteveM** » Fri Apr 06, 2007 1:25 pm

gt2ride wrote:What do you do to keep from making mistakes?

Plan.

Take it slow.

Run through all the movements before you turn the machine on. Be sure that everything goes where you expect it and that nothing hits.

Use stops where appropriate to make sure you don't mess anything up (e.g. run the tool into the chuck).

Check and re-check everything (are you sure the mill head is trammed? Been there, done that, hope not to do it again).

When all the care you have taken fails, figure out why, fix it and move on.

Steve

spro · Post by **spro** » Sat Apr 07, 2007 3:51 pm

Yeh inserts. You don't want to drill that chuck out for a larger size. Stuff happens.You may have heard of a recent mistake where a Vet had one cancerous testicle and went to the hospital and they removed the good one. We can fix metal crap all day. I mean compared to that stuff. Then a guy comes back from a tour in Iraq and is going out with his Babe to dinner or something and a drunk illegal alien plows into them and kills them both. Hey the illegal is fine and at most just goes home. One of three recent cases. All illegals with records of driving drunk,violations,no or false ID and continual roadway murder and who gets a bad day out of that? You did fine work and the counterbores were practice and who did it hurt.? Turn it 45% and redo.

wannabe · Post by **wannabe** » Sun Apr 08, 2007 3:22 pm

I'm taking a machining course in the UK,
These mistakes are now called "improving learning" and we are expected to provide examples of our improvement.
I have a small box full of these now

, but I am learning and improving.

Lee.

SteveM · Post by **SteveM** » Sun Apr 08, 2007 7:10 pm

I'm working on the jaw tops now. Making these out of aluminum (but they can be made from unhardened steel as well).

The things are marked on all sides as to top, bottom, inside, outside, which side gets drilled and which gets grooved.

No way of mistaking this time!

Oh, and I have 4 blanks for a 3-jaw. That gives me one "just in case".

Steve

The Home Machinist!

Machining a backplate - part 3 (or how not to)

Machining a backplate - part 3 (or how not to)

mistakes and main intention

improving learning