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Machining

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If you are determined to make your own planing forms, I would like to suggest what I have done to accomplish this task. I made arrangements to take a machinist course at our local Vo-Tech school at night, once a week, during the winter. If the instructor is anywhere as good as the one I had he can help you with setting up and learning how to use a milling machine. Also the dimensions from Garrison’s book on the planing form were used and the purchase of 3/4" x 3/4" cold rolled steel was even secured by the instructor. I constructed the form using differential screws which to this day are working out quite well. Had only one problem in which I twisted off a carbide tap and then got to use the EDM machine to burn it out without even disturbing the threads that had already been started. Of course we had to modify the EDM to accept a 6' section of steel but again if you are lucky to have a good instructor, which most of them are, these problems are easily accomplished. If you want to discuss this further please use the list and I'll do my best to help.  (Jacques Follweiler)

I'm having a parent of one of my students (I'm a high school math teacher) who owns a small engineering firm make my final planing forms.  The design I gave him is from Thomas Penrose's site. 

They're going to be 6 feet long, and the guy that's going to make them is going to grind the surfaces parallel, drill and tap the holes for the dowels, shoulder bolts, and set screws, and then grind the top and bottom flat.  I'm going to file taper the V-grooves myself.  Are there any special instructions that I should give?  Does anyone suggest any changes to the plans as described on the internet?  I'm going to have him use socket head shoulder bolts and set screws.  Is that what you recommend?

When I get the forms and get ready to file the V-grooves I'll take any suggestions I can get.  Thomas Penrose's site and the info in Wayne's book suggest different ways of going about this.  So anyone who has any experience or better way please feel free to give me some tips.  (Aaron Gaffney)

I wrote an article some time ago for Todd's Tip Site that may answer your questions and expand your ideas.

Don't let the title of the article fool you. These steps work just as well for steel forms. There are also two tools you can build to assist you in cutting the groove. I also have a spreadsheet to help you set up the forms to cut the groove for a slope of .001"/1". Let me know if you want me to send it to you.

I use countersunk pull bolts on my forms for two reasons. First: They give added stability and self centering to the forms alignment, much more so then shoulder bolts. Second: When tightened, they are out of your way.  (Don Schneider)

You might check out my articles in Power Fibers issue 17, 18. I might suggest instead of using the fixed triangle file board I use, use Don Schneider's "File Plane" Don can give more info on it. I finally got to see one,  I think it is better than the fixed file board.  (Tony Spezio)

Has anyone got a program for making forms on a CNC machine? I will  be making some at uni  and need the program.  (Reuven Segal)

"The" program will be different for every set up. What I'm getting at is there is no single way of doing things. Every person has a different way of setting things up. If you have access to a university shop, they will probably have some CAM software such as MasterCAM. Then depending on how you set it up to be machined you will have to write your own program.

Here's how I would do it if I were you. First, the only place CNC is going to be very helpful is when drilling and tapping the holes. Secondly you will either need a machine with 6' of travel (good luck!) or a machine with open sides. A Bridgeport is actually ideal for making forms. The best set up would be if you can find a Bridgeport that's been set up for CNC. The Bridgeports with the old EZ tracker 2 axis CNCs are great for this.

First set up 2 machine vises on the mill. You will want to set the vises a few inches in from the extremes of the travel. Use a 1/10th indicator to make sure they are aligned with the axis of travel as well as each other within better than a thousandth. A few tenths would be best but that just takes a bit more patience and practice.

When you set the vises up measure the distance from the left edge of the left vise to the right edge of the right vise. Do your very best to make that close to a whole inch number, IE 25". That will make things easier later.

Now clamp up one of your bars in the vises and a 1" or bigger fly cutter in the spindle. Make sure the fly cutter can get all the way past the left edge of the bar. Start here and take shallow cuts with a low feed rate until you  completely clean up the top surface. Then slide the bar down and cut again. If your machine is well trammed and you're very careful you should be able to blend the machine marks well enough that you don't feel a bump. Repeat until you have one clean surface on each bar. Depending on how good a job you do with the fly cutter you might not even need to file the bars to smooth out the machine marks. But you want a pretty smooth finish on the bars.

Now clamp the machined surfaces of the 2 bars together with some C clamps and line up the left edge of the bar with the left edge of the left vise. Depending on how you set up your push/pull bolts you can probably drill and tap all three holes with out changing your setup. First center drill all three holes. Then use your pull bolts tap drill and drill through both bars. Then use the pull bolt clearance drill and drill through the top bar, make sure you get all the way through the top bar and use the point of the drill to chamfer the hole for the tap. Then tap the hole right on the machine. You can either power tap, or put the spindle in neutral and do it by hand. Once you have the pull bolt hole done, put the bolt in and snug it up. Move down to your dowel pin hole then drill and ream for your pin. Go all the way through with the drill and stop .020-.030 shy of going all the way through wit the reamer, that will stop your pin from falling out. Put a pin in the hole  then drill your push screw hole. Drill through the top bar and tap the hole most of the way. You will have to come back and finish the tap by hand when you're done. Now just  move down 5 inches and start over. This method requires changing drills and spindle speeds a lot but it ensures everything is in perfect alignment. You'll also have to move your bars down once you get to the end of travel, just like when you dusted off the top of the bars.

Once you have all your holes drilled take the bars out of the vises and take them apart. Clean off all the chips and swarf and finish tapping your set screw holes. take a chamfer tool and remove any burs that may have been created on the holes on the machined surface, then using your pull bolts and dowels, bolt the forms back together. Now you'll have to repeat the first step, but this time you'll need at least a 2" fly cutter. Remove any bolts that interfere with the vise jaws. Machine this top surface down until you not only have it completely clean but until you have nice sharp corners where the 2 bars meet. Do that to both sides.

Now comes the part I hinted at earlier. Take that measurement from the outside edges of the  two vise and get some gage blocks. If the vises are 25 inches apart get 2 gage blocks that are .025 different in thickness, IE a .100 and .125 blocks. This will give you the .001 drop per inch in length.

Place the shorter block at the left edge of the left jaw and the taller block at the right edge of the right jaw. Now you'll need a 60 degree chamfer tool. If there is any flat on the point of the tool you'll need to spread the bars apart by at least that amount. I would suggest you buy some precision thickness washers available from places like McMaster-Carr. Now set your forms on the two blocks and center your cutter in the opening. Move the table as far left as you can so that your cutter is at the highest point that it will cut during that set up. Then lower the cutter until it just barely touches the edges. Move back to the left at least 10 inches and lower the cutter .010 and feed the bars under the cutter. Once you get to the end of the travel lift up the cutters. Now move 20" to the left and drop you cutter .020 from your original zero and repeat. Keep going until you get all the way to the edge of the bars. When you get there lower the cutter until you just barely touch the edges and go all the way to the end of travel. If you want a very fine tip groove only go down another .010-.015 from that depth. The last pass you take should only remove .001-.002 of material so you get a nice clean finish. Now slide your forms down and repeat until the grooves blend together.

Do your tip side first in case you make your groove too deep you can just turn it into the butt side. Now just flip the forms and do the other side.

I'm sure this all sounds very tricky and difficult but when you get on the machine and start cutting metal its not too bad and you could probably get it done in a day.  (Mark Shamburg)

About the dowel pins. I have made three sets of forms and don't use dowel pins. Instead I use flat head countersink screws on the "pull" side and headless Allan set screws for the "push" screws. I find I have no problem with alignment. The taper in the countersink seems to keep things aligned. I also put the "push" Allan head set" screws on one side and flat head countersink "pull" screws on the other side, makes for easy setting the forms with an Allan wrench on each side at the same time to open or close the gap. The "set" screws  are buried in the form and the flat head  screws are flush on the other side. No knuckle scrapers.

I only had a drill press to use when I made mine.  (Tony Spezio)

Has anyone on the list used powered workshop tools to manufacture forms? I have been toying with the idea of using a CNC machine to make one long swipe along forms that have been bolted together already. That way, they are perfectly aligned from the beginning and one angled swipe with a 60 degree tool piece should be able to produce a perfect set. They can then be flipped, again perfectly aligned form the beginning, to produce the tip section.

Does anyone have any comments regarding this stroke of brilliance??  (Reuven Segal)

Obviously that is the logical way to do it.  Considering your access to metalwork tooling, you may be able to do it.  HOWEVER, it is not apparently just as cut and dried as it may seem.  I said to the man who made mine that all he had to do was set up his axes and then run the 60 degree tool, deepening .001 for every 1" travel, turn it over and do it again.

But in fact he didn't have anything civil to say to me for quite some time after this episode.

Which gives rise to the McKean Principle - "If you have a friend who is a machinist, and you want him to make you a set of planing forms, and if you still want a machinist friend at the conclusion of the exercise, you should go and get another friend who is a machinist before you start."   (Peter McKean)

The main problem with using that type of equipment is finding someone that has a machine that can travel 60 inches plus.  I had an Engineer friend of mine put my planing form design into CAD format and to make a long story short, after 2+ years of looking, I'm still trying to find someone that has the machine and will not charge me $1,000 to make my form.  Someone that has access to this type of machine and would be willing to do it on the side for you is a friend you should hold on to dearly!

This type of equipment in my area runs at $250 hr plus set up cost.

This would be the preferred method though, you are correct.  (Scott Bahn)

I assume you're talking about machine tools such as a milling machine.

I think you'd be pretty lucky to find a machine with a long enough travel to do the entire groove in one swipe. Also, you'd probably want to take depth cuts anyway. What you can do is line up two vises in a row on the table of a milling machine and slide your bars down. If you've got the machine well trammed in and line the  vises  up  within  a  few  tenths  of  a   thousandths (.0001-.0003") then you will have no trouble blending in the multiple cuts. (Mark Shamburg)

I've given myself headaches thinking about making forms.  Because my trade is woodworking, I'm toying with making set wooden forms for some of the more requested rods that I do and still use the adjustable forms for the bespoke rods.

I've got access to an over head router and I spent a fair time looking at the process you described, basically by setting the ungrooved forms gradually opening (or closing) You should be able to cut the taper in one pass.

The main problem is keeping the cutter centered on the forms, if you run the form against a straight fence the cutter takes off a straight cut.......

So the plan is to make up a long adjustable tapering fence that the actual form runs with past the cutter (It's a potential can of worms) I should be able to then adjust the fence to produce any variation of taper.

ALL CLEAR ??? (Luke Bannister)