Machining plan

As a mental exercise I wanted to write up a plan to machine a simple part. It wasn't the idea to have someone else do the mill work, I just wanted to see if I could do the operations in my head and write it out accurately and functionally. Here is the first draft. After reading through it I see a number of small problems, bad practices, better ways of using the DRO's features and better ways of communicating. So, that got me to thinking about how to plan machining operations and provide the right numbers from the drawing to a spreadsheet or such, trying to minimize the "Art" in machining. To actually do this part, I would just pin up a drawing on the mill and make chips without too much thought. For this simple part, no big deal, and the chance of screwing it up is minimal. However, as parts get more complicated, the chance or screwing it up or wasting a bunch of time increases. It seems to me that a good plan is a good idea. I have no idea how to do this planning and I'm wondering if there are resources available. I think I also want to roll good planning into the drawings trying to imagine tool paths, DRO readings and order of operations. So, it seems I not only need to re-learn over how to machine stuff, I need to re-learn how to draw stuff. This little exercise has been very revealing.
Here's a pix of the part in the dropbox: http://www.metalworking.com/dropbox/ob_cutter_arm.jpg
0. Prepare rectangular blank. 1. Bandsaw the upper left corner leaving .01" to .02" 2. With the left corner of the Kirt vise indexed to X=0, Y=0,(memory "0") on the DRO, support the blank on parallels with the sawed corner up and left even with the indexed vise corner. 3. With a 3/4" end mill, finish machine the blank's corner. A. Clean-up enough of the bottom of the notch to measure the thickness. B. Mill the bottom of the slot to the finished dimension to the right until the DRO reads .625" thus the cut will be 1". Mill the Y axis to remove the radius left by the end mill. 4. Clamp the blank face-up on parallels with the notch to the left rear. 5. Move the table to: X=.750", Y=.-1.4982" and drill using a small starter drill. Change bit to .250" and drill until the flutes are a bit deeper than .250" set DRO to zero on upper left corner of the pocket. 6. With a 1/2" end mill, mill out the carbide pocket. A. With the DRO at Y=0 and the mill off the blank to the left, move the table to the left until the DRO reads X=.480" cutting to .125" deep. Move the table to the right off the blank. Move the table back to Y=-.250 and repeat cutting .250" on the y until Y=-.480". Repeat until depth = .250" B. Using a 1/4" end mill, clean up the sides of the pocket to X=.625 and Y-.625". 7. Zero the DRO back to home position and move table to the bore at X=1.866" Y=-.6875" 8. With a small center drill, start the hole. Drill through with 1/4", 1/2", 5/8", and 11/16". 9. Bore to .749" with adjustable boring head and small boring bar.
Tooling: End mills: 3/4", 1/2", 1/4" Small and medium-large Starter drills (Combined drill-countersink) Boring head with small boring bar. Parallels Micrometer or caliper Bore gauge for 3/4" BFH

Haven't personally done process planning since I was a new-hire mechanical engineer in the orientation program at my first full-time job back in the mid 1960's. Here is a Google search on 'process planning'. http://www.google.com/search?hl=en&q=%22process+planning%22 It appears there are resources out there, possibly way beyond your immediate needs. The whole point of planning, as you have already recognized, is to spot inconsistencies of approach and encourage the identification of alternatives.
I'd suggest as your next step you explore the combination of text with in-process drawings. It is easy to insert, reposition and resize graphic images in MS Word ('Insert' + 'Drawing' + 'From File'; right click on image to edit). You can then create drawings of how the part should appear at key intermediate steps, very helpful if you need to communicate the process to others and even to aid in your own visualization of the progression of process steps. You will soon run up against the resolution limitations of raster graphic images (like *.jpg, *.gif, *.tif, *.bmp) and will want to become familiar with vector graphic formats (like (*.dxf, *.cgm).
David Merrill
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Great idea! It's easy to undo features and cuts on the finished part in Solidworks and create a progression series like you mention. Each step with inserted text explaining each process step would simplify the models in stages and would be easy to communicate and standardize the work. Great idea!
You will soon run up against the resolution limitations of
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I only use the .jpg to post or e-mail an image.

Several things come to my mind.
How many parts are you talking about?
Why don't you have all the information on the drawing? At a quick glance you don't call out the location of the hole, or the tolerances.
Also the resolution of the picture, at least on my monitor, does not allow me to read all of the dimensions you have given.
On the pocket area you don't call out how deep you want the clearance radius.
I suppose I could extrapolate some of the information from reading the text, but it seems to me that any time saving you expect from planning out each step as you have will be lost having some one figure out what you want from what you have provided.
It is OK to try and take out the "Art" of machining to use unskilled labor to run the machine for production runs, but the "Art" is going to be there in the person the sets up the job, and it would seem to me that listing it out the way you have would take more time and effort than a clear standard 3 view print.

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Well, the image I posted is the model, The drawing is derived from the model in Solidworks. I just threw a pix and a few dims, in order to communicate a general feel for the part. (It's a simplified version of a real part) One would work from the drawing that is very robust.

On Fri, 9 Mar 2007 00:08:07 -0800, "Tom Gardner"
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Wow!
Another approach:
Have idea. Make sketch on back of junkmail envelope. Find a piece of metal. Stick it in vise or chuck. Begin selective reduction of size of piece of metal. Replace broken cutter while uttering incantations. Tell Milady I shall try to utter my incantations less loudly. Continue machining until part works and/or fits. Measure part, dimension drawing. Toss drawing, sketch what Mark II might look like.

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That's the way I've always done it...I'm trying to improve!

On Fri, 9 Mar 2007 16:05:42 -0800, "Tom Gardner"
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That's too much like work. Ah'm a reetahrd guy, untrainable!

On Fri, 09 Mar 2007 14:05:46 -0600, with neither quill nor qualm, Don
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That's how my woodworking goes, Don. I like it!
.-. Life is short. Eat dessert first! --- http://www.diversify.com NoteSHADES(tm) laptop privacy/glare guards

I've got to do this more than quite a bit, and I've learned some of the tricks that make it easier. I train other students to use the basic machine shop equipment to do specific operations as a predecessor to teaching them to make actual parts. I have found that the hardest part is actually breaking down a complicated part into the set of operations that you or I do naturally. I also have to deal with communications between students, for example, it is not uncommon for one student to be squaring the parts, then leaving them for a different student to drill the hole pattern, etc. Often they are not working in parallel, but rather one student will work for several hours, leave, someone else takes up whatever they were doing, etc. Although we have good facilities in our own shop, we often go to the local City College to use their large shop, simply because their multiple machines and larger lathes make multiple parts much faster with 2-4 students working. One technique I borrowed from woodworking to keep track of parts during multiple ops is the standardized marking of reference sides, edges, etc. I have also been known to spot drill a small hole in one corner of the part, from which all other features are referenced (this could also be a distinguishing feature, like a unique tapped hole, for example). The last think I noticed at the end of your list, the necessary tooling, is an issue that I have attempted to tackle. With literally hundreds of parts, often coming from tens of different drawings and a dozen or so different materials, all in a short time frame, I go through and look at each job as it is finalized, and make a list of what kind of tooling I think it will take to get things done. In our shop, where all of the tooling is at hand, it is only useful primarily as a check and to see what parts will use what kind of tooling. At the City College, where all of the tooling is in a separate toolroom, forgetting tooling and walking back and forth to the toolroom all day long wastes a significant amount of time. I give the lists to the toolcrib attendant (who happens to be a student with an after school job), and he puts the tools in little bins divided by part. Then I have the students grab the box for the part they're working on. So far these techniques seem to be working for me, maybe they'll give you and others some ideas, ww88 Lead Student Machinist/Shop Manager Los Altos High School Robotics Team Los Altos, CA

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Sorry for the long post. I think I kinda violated NG protocol with that one. ww88

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No. It was, refreshingly, on topic, and if you're on topic, any length (text) will be just fine. Pictures are not, at least not directly. Quoting the whole thing in your self-followup might be a bit on the edge, but it's nothing compared to the endless posts blithering at the (opposite but equally stupid) wings of politics.
Hundreds of parts made in a short timeframe by different students - makes a good case for getting the measurements right (and the drawings before that).

wrote:
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Thanks for the support and heads-up. Google Groups hides the quotes for me, so I don't notice them, but I'll make sure to check for next time. ww88

There's no reason to apologize for any length of appropriate-topic, metalworking related comments. Your posts are informative, and my only suggestion would be to use some line breaks (enter, enter key) to break up the text into some paragraphs.. it makes reading them much easier.
WB metalworking projects http://www.kwagmire.com/metal_proj.html ...........
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Okay Thanks

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It's called Methods Engineering, and it involves the methods engineer taking a drawing and writing up the steps (instructions if you will) to make the part. The methodology will include all the steps, from bar stock or casting to finishing.