Any Machinist types out there?

[Joeaksa]

A friend of mine is needing some machine work done. Its very special stuff and normally would not need a lot of these done, but could turn into a small money maker if it took off.

He needs some of these made:



Its the yellow plate on the bench in the center.

Another view:



Anyone on the board have the capability to make something like this? If so any idea on the cost to produce say 6 to 10 of them?

Thx,

Joe

[Tim Hancock]

Joe, I will check with the machinists at work to get a price. I am assuming you want these out of aluminum. If so what type? 2024t3? I they have the time to sneak a "govt" job in, I would need a few missing dimensions such as outer corners to define how many degrees of a circle these parts need to be and what size holes need to be drilled or reamed. Our normal shop rate at work, would be a bit pricey, but if I can get it done on the side, it should be pretty reasonable.

I will check back on Monday when I am at work to see if you still need this done. I could make these myself at home using my old lathe, but milling them at work on a CNC mill would probably be the easiest way to do this and accurately placing the holes will definately be easiest with a milling machine.

[Joeaksa]

Tim,

Between us two (know that no one else will read this thread) this is a part for a McDowell starter on a 1946 Aeronca airplane.

The parts are not available and we are trying to build several using the blueprints. We have blueprints with exact measurements and could get them to you. Not sure if its aluminium or steel but bet its not steel considering that its on an airplane.

If you could work out a run on a CNC and the price was descent I would finance a run of 10 or so. These will not be PMA or approved in any manner, so not to worry about any liability.

Thanks,

Joe

[Joeaksa]

Tim,

Just heard back from the guy needing these. (I may need a couple as well so throw my name in the hat)

Here is the info on the parts.

~~~~~~~~~~~~~~~~~~~

Joe, Bill Pancake used carbon steel for these. The vibration and fact that the McDowell Air Starter is all steel makes steel the best material. I would be concerned with aluminum, especially with the McD being connected with taped/threaded 10/32 machine screws in 3 outermost of arc holes. The 2 inside most of arc holes are clean drilled 3/16" diameter, not threaded. These 2 inside of arc holes are for 3/16" course-threaded bolts that only thread into the prepped C-85 nosepiece. This typical Lycomming bolt only passes thru the mounting plate - not threaded into the mounting plate.

I was considering using 304 Stainless, but its availability and cost was a bummer. I would still be a best choice over carbon steel.

The plate starts as a 1/4"thickness. A 8" x 8" square plate would be a good start. The inside of the plate is then machined with a 4.00 " hole in the plate center.

Then mount the plate with the center hole on a lathe using the inside hole chucking fixtures. Next, machine cut the outside of the plate to leave a disc with a 7.20" outside diameter, 4.00" inside hole x .25" thick.

3rd step would be to machine one outside face down to the .09" thickness to the dimensioned width with the 30 degree bevel.

4th step is to remount the disc chucking from the outside and machine the opposite face from the inside with the final thickness .09" and the opposite face of the 30 degree bevel. The bevel is therefore about .09" also. The total opposite face-to-face depth is .025", necessary for the McDowell to mount in the proper position with the C-85-8F flanged crankshaft.

The hole centers and cut lines between the 3 arcs need to me carefully marked on the machined disc. The disc is the cut into 3 equal arcs as dimensioned, WITH A SMALL UNUSABLE SHORT ARC SCRAPE PIECE LEFT OVER. The 5 holes are then drilled in each arch in 2 different sizes, and the 3 outer holes are tapped/threaded as 10/32. The dwg shows only 2 arcs being cut, but Bill Pancakesays he ended up getting three usable arcs cut from a single 7.20" diameter disc.

The only drawing available is the one I have already sent you. However, I'm attaching 2 halves of the drawing for clarification. On the top of one of the 1/2 sheets there are 3 dimension lines, 3.281" , 2.593" , and 3.750". The 3.281" is missing from some of the scanned 1/2 sheet images. It is shown clearly on the document with the single arc piece laid on top of the details in the photo.

Here is the blueprint and I have a larger version I can email you.

[charleskieffner]

val-tec machine tempe-c/o dave valente worked and raced with dave when we were young. short run prototype shop. dave worked at garrett for years w/me until opening his own shop. manual and cnc. if you take this part to any standard shop they will drill you thru the eyes on cost.

tell dave i sent you. or i'll go in and introduce him to you. also his #2, guy is an ffl mfg. and builds some really nice rat a tat tats. dave does short run stuff for everyone here in town. i think he is even a faa certed shop.

[Tim Hancock]

I will check into it Monday and also draw/dimension it properly on CAD. I will post it for you to have your friend approve it. If the guys at work have time and are willing, I will get you a price. If not, at least you will have a decent drawing to take to local machine shops. FWIW, the 3/16 dr thru on the inner holes will need to actually be a #12 (.189" dia) or #11 (.191" dia) drill to allow a slight clearance for a #10-24 (he mentioned a "3/16" coarse fastener) to pass thru it.

If it is steel, the logical choice would be to make it from 4130 steel plate, which I can get.

I am a special machine designer (by day) for a custom automated machine design and build company and we have a well equipped shop that can easily make these parts. I just need to see if I can talk one of the machinists to help me out "off the company clock", as our standard shop rate would make this job too pricey in low quantities. We occasionaly do strictly machining jobs, but we cannot compete with strictly machine shops. IOW, if I can get you a "good buddy" discount I will, otherwise it will be too costly for our shop to do it "above the table".

[Joeaksa]

Tim,

Thanks and pls let me know how it goes.

Joe

[Tim Hancock]

Joe, the dimensions for the holes on your drawing are not working out.

I will try to explain: Typically when holes are placed on a round flange, they are drawn on a bolt circle of a certain diameter (radius). For example, on your drawing the inner two 3/16 dia drilled holes are shown drawn on a 2.531" radius, but then they are also dimensioned using x/y dimensioning (3.250" vertical distance and half of 3.750" from center for the horizontal distance). If I draw them on cad using the x/y dimensions, then they will not be on the 2.531" radius (end up being inboard of 2.531" rad by .050".....quite a bit).

The outer 10-32 tapped holes are only dimensioned using x/y dimensions and when drawn, they are not on the same bolt circle (they are off by about .006").

Whoever measured this needs to re measure it, as the inner holes are off by quite a bit. I would accurately measure the vertical distance between the two inner holes, then confirm the radius (bolt circle). For the outer tapped holes, I would do the same (measure the distance between the top and bottom holes, then confirm that the 3.281" dimension is the correct radius.

Cad does not lie, the outer holes as drawn might work, as they are close, but the inner holes are dimensioned incorrectly (either the radius listed is wrong, or one of the x/y dimensions is wrong).

By the way, the cross section is wrong also, if the vertical dimensions are correct from the ID placing the offset locations, then the 30 degree angle is wrong (no big deal) the overall height is wrong though as 7.2-4 divided by 2 = 1.6" not 1.687" as listed. I am guessing the OD of 7.20" or the ID of 4" is not quite right, while the 1.687 is corect if that is what he measured the actual part at.

[David]

When I reverse engineer parts I check for two things: 1) almost everything is designed to nominal dimensions, so if you get a bolt circle of 2.531*2" that's suspect; (2) when I plot the drawing out in 1:1 scale and lay the original part on the drawing it should match perfectly.

[Tim Hancock]

Originally posted by 125shifter
when I plot the drawing out in 1:1 scale and lay the original part on the drawing it should match perfectly.

I do the same

Unless you want parts that do not fit, it would be wise to remeasure the parts accurately, or send me or someone else a part to measure accurately. A place to start would be to draw a doughnut at 7.200" od x 4.000" id and lay the part on it to confirm the diameters.

Let me know Joe. I tried your cell# from last summer at the Aeronca flyin...No joy. If you want, you can PM me your current cell # and I will give you a buzz to discuss it further.

[jim72911t]

Joe,
Those parts could be made on a 2-1/2 axis CNC milling machine quite easily in two operations with minimal fixturing, using rectangular stock. The only issue with using this method is the relatively large amount of material that would need to be removed to arrive at the finished shape, but you'd be surprised as to what modern cutters are capable of doing with regards to quick metal removal.

I've always been a proponent of making a part with the least amount of steps (fixtures); each added step adds to cycle time and increases the possibility of error. That being said, it also depends on what kind of machines and tooling one has at their disposal.

I'm not trying to step on Tim's toes here, as I don't have the machine time available in our shop for such a small run, but I'd be happy to send you a ballpark quote for reference. I've been reverse engineering parts for years now, and handle all the quoting for our shop.

Good luck,
Jim

[Mr Beau]

www.emachineshop.com may also be a good option for a project like this.

[Joeaksa]

Back on the ground now, was in London before, now finally back at home.

Have emailed the guy who needs these and awaiting an answer.

Joe

[Joeaksa]

Does this help any?

[Tim Hancock]

Don't worry about stepping on my toes Jim, my involvment is strictly as a favor to Joe, not as a money maker.

FWIW, our Fadal cnc programer said that our shop would "officially" quote about 8 hrs to make 9 of these parts. He said he would start with a square 1/4" plate and put all the holes in and cut the od and id in the cnc milling machine, then make a face plate to chuck in a cnc lathe with #10 clearance holes to attach the blank using 10-32 screws thru the back plate threaded into the outer 10-32 tapped holes. He would then cut/face the inner flange. Next he would remount the the plate again using the 10-32 screws and cut/face the outer step.

He considered doing it all in the cnc mill, but cutting the 30 deg angle was more easily done on a lathe in his opinion.

If Joe still wants this done , I figured a way that the machinist at work can make me essentially a drill fixture/back plate that would allow me to do the job at home on my small lathe and drill press. I would need a correct dimesions however as it would not make sense to waste a bunch of time making "bad" parts only to have to redo them all again as well as making a new fixture etc.

[Tim Hancock]

Originally posted by Joeaksa
Does this help any?

Not really, as the numbers on the print are still the same if you re-read my earlier post, you will see where the discrepencies are especially in regards to the inner hole dimensioning of the radius and the x/y dimensions and the id/od difference compared to the cross section height dimension.

PM me your current cell number Joe and I will attempt to explain it to you more clearly.

[Tim Hancock]

Update:

I am shipping 8 of the completed parts to your buddy today Joe.
I ended up having a drill fixture/lathe face plate fixture made on a CNC mill by one of our machinists, then I roughed out some steel plates, center drilled all the holes with the drill fixture, rough cut the center hole with a hole saw, drilled and tapped all the pre-center drilled holes, mounted the plate to the fixture which I chucked up in the lathe for turning/facing/contouring, then I flipped the plates and did the other side. Finally I mark the disks and cut them each into 3 finished parts then deburred them.

Took a fair amount of time. In a perfect world, I would make these from bar stock all in a CNC machining center, but it was kind of fun and a bit of a challenge for me to make them in the lathe as I do not get to play in the machine shop very often.

[Joeaksa]

Tim,

Looks very nice! Reminds me of my old school days when I had a machine shop to work with. Nothing like making a tool or part out of a bare piece of metal or wood.

Will email with you on the details.

Thanks again!

Joe A