Would you use plastic airframe templates?

[old man emu]

If you were building a plane from plans, would you consider using templates made from hard plastic to check fit and hole alignment?

 

What I am talking about are airframe fittings produced using 3D Printing techniques. Basically the process involves drawing the part using a CAD program, then processing the drawing file to create instructions for a machine, similar in appearance to a CNC mill, to create the object by laying down filaments of molten plastic until the object is complete.

 

The object would be true to the drawing. It would contain all the holes that fasteners would go through in the final product, and would have all the correct bends if that was what was required. The plastic item could be used to check for fit, or used as a drilling template. The object would be made of ABS plastic, which is the same stuff the LEGO blocks are made from.

 

Finally, if the template was correct, the drawing file could be sent to a CNC machinist to make as many of the fitting as required from the specified metal.

 

The process can also be used in the process of making replacements for damaged components such as cover plates, knobs and switches if a person was restoring a plane etc.

 

Old Man Emu

 

 

[winsor68]

The possibilities really are endless for this technology...mind boggling really.

 

 

[paulh]

I would think that if someone had some complex parts to make or a kit suppliers drawings were not that good an inexpensive 3D template would be very helpful and assist with build accuracy.

 

Designers could use 3D printed parts to check their ideas before committing to CNC machining etc. As I understand ABS plastic is dimensionally stable and reasonably tough.

 

Sounds like there is some potential business there for you for a whole range of times.

 

 

[Guest Maj Millard]

The operating program that runs the CNC mill (computer numerical control) to make a part, is either inputted by simply typing the finished dimensions into the operating program, or by measuring a part using a special CNC measuring tool within the machine itself. This initial part needs to be super accurate, as the mill will then produce the new parts exactly the same size, unless the measurements are adjusted manually by the operator.

 

Often CNCs will operate on tolerances as low as 2-3 ten thousands of an inches on critical dimensioned parts. Thermal extension of the machines themselves often have to be taken into account, and warm-up program's and additions to operating measurements are often used for the first couple of hours in the mornings until the machine has " fully warmed up". These 'added' measurements are then removed and the base program used. On many CNC mills and laths ceramic parts are used in lue of steel to minimise this thermal-expansion problem. Actual cutting-tool wear is also a problem and the machine automatically changes tools often, when it detects finish demensional change outside of pre-set tolerances . CNC machines are extremely accurate and consistent, capable of producing hundreds, and even thousands of parts exactly the same when all is well.

 

Moulded plastic may be suitable as initial measurement models, but it would all depend on just how close your measurements and tolerance requirements are...................Maj...

 

 

[sain]

Its an interesting thought, especially as there are online print shops now that do 3d printing, with better than hobby grade machines. As I understand it you design your parts using cad and send them off to be printed. When they come back, test them out and make sure they are right, then send the cad file to your cnc people (also available online if you don't want to cough up the cash for a machine) to cut the parts out.

 

I've got a hobby grade CNC milling machine, which I'm only beginning to learn to use, and it works pretty well. I'd be inclined to mill the test pieces out of plastic or wood rather than 3d print them - unless you really need the 3D. My understanding is that 3d printing is very slow, and you are size limited a lot more than with a CNC machine, due to parts warping as one end cools before the machine gets to the other. It may be less of an issue for SLS (selective laser sintering) machines than it is for FDM (fusion deposition modelling?) machines.

 

Where I'd see it useful is testing the assembly process. Some of the better CAD packages let you see if the pieces will all fit together, but there are not many I can think of that will test to see if you can actually assemble something without breaking it. "Can you get the required tool into the space?" testing and that sort of thing.

 

 

[old man emu]

Moulded plastic may be suitable as initial measurement models, but it would all depend on just how close your measurements and tolerance requirements are...................Maj...

I'm talking about brackets and plates that might be used on the airframe or wings. If the dimensions on the drawings for these sort of parts are, say, to the nearest 1/8", then the greatest accuracy you should look for is half of that unit, which is 1/16".

 

If you were measuring up parts to cut from stock, your accuracy would depend on the accuracy of your measuring tool. Therefore, you have to accept +/- 50% of your smallest graduation of your measuring tool. With a CAD measurement, the computer will use the measurement you type in to the program. I admit that the machine doing the making of the part will have "slop" in its movement, but since each movement is usually very small, the finished product is not likely to drift outside the +/- 50% error.

 

The idea of using 3D printing is to produce a test piece at low cost so that any modifications required will also be low cost.

 

OME

 

 

[RickH]

If you use Autocad Inventor or similar such programs they will allow you to test fit parts in virtual reality some of the other autocad programs will also do the stress annalisys for you and as for the measuring tolerances if the dxf file produced by auto cad is fed directly to the cnc machine then it will be as perfect as the wear / built in tolerances of the machine will allow and that would be the only impediment to accuracy. My experience ( reasonably extensive) is that any discrepancy will be less than you can measure even with vernier calipers. Apart from having used this gear in general engineering I did a fair bit of this kind of work when building my bird. Ie all wing rib blanks( and many other parts) cut on waterjet and cnc milling machines.