chris_booth
01-22-2006, 06:26 PM
I’m particularly interested in learning more about jigs, techniques, suggestions, concepts etc. for making objects that need machining from every side. I’m thinking of objects that are pretty small in every direction – say perhaps up to a foot cube.
Maybe this initial concept for a jig to be used with the ShopBot indexer will get the idea across. My interest is aimed in particular at making 3D prototyping easier.
I’ve been doing some work with powerful 3D CAD (Solidworks) integrated with powerful 3D CAM (SprutCAM) and am beginning to think the following:
with suitable jigs and methodology, it should be possible to set up a combined hardware/software general approach that will let us machine every side of a block within the size of our system, and in a reliable and efficient manner.
I haven’t been using an indexer yet or any particularly fancy jigs – but if a good concept for a jig and methodology comes up it would be easier to take advantage of it by planning the machining process by putting a model of our required 3D object inside a model of the special jig I’m looking for and planning from there.
Anyway here’s a “starter for 10” concept jig for the ShopBot indexer....
416
1) Prepare a volume with a cylindrical peg to load in the jaws of the indexer jig. (Perhaps I should have made this model of a die without the rounded corners and added the rounds when the holes were made in each face!)
417
2) Machine the first face.
418
3) Rotate to present the second face.
419
4) Machine the second face.
420
5) Rotate to present the third face.
421
6) Machine the third face.
422
7) Rotate to present the fourth face.
423
8) Machine the fourth face.
So far nothing out of the ordinary. Support at the opposite end could be used with the standard ShopBot tailstock – with a custom-made form to meet the part. For example, if we had machined a flat on the face opposite the cylindrical peg when we prepared the volume to load in the jaws of the indexer jig, we could use a flat-fronted indexer tail live center.
424
9) Next we open the hinge in this 1st part of the jig. Our indexer is holding this hinge axis in a horizontal plane.
425
10) I envisage over-opening it i.e. beyond 90 degrees, placing a machined “spacer” of the required length on the indexer rail, setting the hinged part down on the machined top of this spacer and clamping.
426
11) Machine the fifth face.
I’m not happy with the difference in height (Z) between the machining of this face and the first four. But the important thing is...we know where it is! By that I mean that the file or files prepared to machine face 5 will be (or at least should be – I wonder what sort of tolerance we could expect from a beast like this?) at a known 3D offset from the files used to machine the first four faces.
Theoretically, with a jig of this nature, you could prepare a ShopBot “master” file that runs the entire machining of the 6 faces (at least “per cutter”) and the master file would call the individual files to run, with their 2d or 3D offset, and probably move the gantry out of the way and wait for a keyboard input before continuing – an input that you’d give when you’d made the required modification to the jig set-up.
427
12) Remove the (invisible) support and...
428
13) Close the hinge. There would be a locking device (not modelled) to keep this closed securely as required!
429
14) Bring in the 2nd part of the jig by sliding it along the indexer T-slot. In this model I put this 2nd part of the jig on another indexer. In the way we’re using it, it could just as well have been without the indexer! Anyway...
Because we prepared our entire machining strategy in a 3D CAD software where we worked with both the object we are planning to make and the jig set-up we’re using – including the relative positioning between jigs and part – we were able to prepare made-to-measure form-fitting surfaces to put in the clamp jaws of the 2nd part of the jig.
This might seem difficult, but in a good 3D CAD system, working with a standard procedure, the steps to design these made-to-measure surfaces can be made pretty efficient. We can set our “virtual clamp jaws” where we like – simulating what we will later do - extrude the base form up to and into the object, then cut it back by what can be called a “boolean subtract” (but different 3D CAD systems typically call it different things), and then plan the CAM to cut our set of made-to-measure form-fitting surfaces.
430
15) Bring it right in – our design of clamp surfaces could either by so that we simply push the 2nd part of the jig right up to meet the object (i.e. the surfaces will be supporting the object from underneath when we open the 2nd hinge) or we move the jig precisely to a known distance from the other jig (known because we modelled it all together) for clamp surfaces that will not be supporting underneath.
431
16) This example is the second of those types mentioned above. The clamp surfaces do not supprt from 100% underneath. In this image the 2nd part of the jig has been moved to the precise place required, but the clamp surfaces are not yet engaged. The 2nd part of the jig is then secured (i.e. so it can no longer slide along the indexer T-slot rail).
432
17) Now the clamp surfaces are engaged. This concept model uses 2 perpendicular sets of clamps who’s faces are always the same distance from a central plane. It may be preferable to use a type of clamping that rotates in rather than moving in linearly.
433
18) And with the 1st part of the jig unattached and moved away, we can open the hinge on the 2nd part of the jig.
434
19) Note the invisible support placed manually between the indexer aluminum rail and the underside of the jig.
435
20) Remove the cylindrical peg we used to load the part in the jaws of the indexer jig.
436
21) Machine the sixth face.
437
22) Close the jig...if the model requires more than one cutter we’ll have to do more work – and we’ve already cut off our cylindrical peg! Looks like we’ll have had to organise our cutting “per cutter” for faces one to five together, and then “per cutter” for the sixth face after the “hand-over” to the 2nd part of the jig.
438
23) Remove the finished part
439
24) Leave everything and go and make a cup of tea. Then start measuring to find out if its within tolerance and visually inspect it to find out if you’ll be able to hide the imperfections by hand-finishing.
Maybe this initial concept for a jig to be used with the ShopBot indexer will get the idea across. My interest is aimed in particular at making 3D prototyping easier.
I’ve been doing some work with powerful 3D CAD (Solidworks) integrated with powerful 3D CAM (SprutCAM) and am beginning to think the following:
with suitable jigs and methodology, it should be possible to set up a combined hardware/software general approach that will let us machine every side of a block within the size of our system, and in a reliable and efficient manner.
I haven’t been using an indexer yet or any particularly fancy jigs – but if a good concept for a jig and methodology comes up it would be easier to take advantage of it by planning the machining process by putting a model of our required 3D object inside a model of the special jig I’m looking for and planning from there.
Anyway here’s a “starter for 10” concept jig for the ShopBot indexer....
416
1) Prepare a volume with a cylindrical peg to load in the jaws of the indexer jig. (Perhaps I should have made this model of a die without the rounded corners and added the rounds when the holes were made in each face!)
417
2) Machine the first face.
418
3) Rotate to present the second face.
419
4) Machine the second face.
420
5) Rotate to present the third face.
421
6) Machine the third face.
422
7) Rotate to present the fourth face.
423
8) Machine the fourth face.
So far nothing out of the ordinary. Support at the opposite end could be used with the standard ShopBot tailstock – with a custom-made form to meet the part. For example, if we had machined a flat on the face opposite the cylindrical peg when we prepared the volume to load in the jaws of the indexer jig, we could use a flat-fronted indexer tail live center.
424
9) Next we open the hinge in this 1st part of the jig. Our indexer is holding this hinge axis in a horizontal plane.
425
10) I envisage over-opening it i.e. beyond 90 degrees, placing a machined “spacer” of the required length on the indexer rail, setting the hinged part down on the machined top of this spacer and clamping.
426
11) Machine the fifth face.
I’m not happy with the difference in height (Z) between the machining of this face and the first four. But the important thing is...we know where it is! By that I mean that the file or files prepared to machine face 5 will be (or at least should be – I wonder what sort of tolerance we could expect from a beast like this?) at a known 3D offset from the files used to machine the first four faces.
Theoretically, with a jig of this nature, you could prepare a ShopBot “master” file that runs the entire machining of the 6 faces (at least “per cutter”) and the master file would call the individual files to run, with their 2d or 3D offset, and probably move the gantry out of the way and wait for a keyboard input before continuing – an input that you’d give when you’d made the required modification to the jig set-up.
427
12) Remove the (invisible) support and...
428
13) Close the hinge. There would be a locking device (not modelled) to keep this closed securely as required!
429
14) Bring in the 2nd part of the jig by sliding it along the indexer T-slot. In this model I put this 2nd part of the jig on another indexer. In the way we’re using it, it could just as well have been without the indexer! Anyway...
Because we prepared our entire machining strategy in a 3D CAD software where we worked with both the object we are planning to make and the jig set-up we’re using – including the relative positioning between jigs and part – we were able to prepare made-to-measure form-fitting surfaces to put in the clamp jaws of the 2nd part of the jig.
This might seem difficult, but in a good 3D CAD system, working with a standard procedure, the steps to design these made-to-measure surfaces can be made pretty efficient. We can set our “virtual clamp jaws” where we like – simulating what we will later do - extrude the base form up to and into the object, then cut it back by what can be called a “boolean subtract” (but different 3D CAD systems typically call it different things), and then plan the CAM to cut our set of made-to-measure form-fitting surfaces.
430
15) Bring it right in – our design of clamp surfaces could either by so that we simply push the 2nd part of the jig right up to meet the object (i.e. the surfaces will be supporting the object from underneath when we open the 2nd hinge) or we move the jig precisely to a known distance from the other jig (known because we modelled it all together) for clamp surfaces that will not be supporting underneath.
431
16) This example is the second of those types mentioned above. The clamp surfaces do not supprt from 100% underneath. In this image the 2nd part of the jig has been moved to the precise place required, but the clamp surfaces are not yet engaged. The 2nd part of the jig is then secured (i.e. so it can no longer slide along the indexer T-slot rail).
432
17) Now the clamp surfaces are engaged. This concept model uses 2 perpendicular sets of clamps who’s faces are always the same distance from a central plane. It may be preferable to use a type of clamping that rotates in rather than moving in linearly.
433
18) And with the 1st part of the jig unattached and moved away, we can open the hinge on the 2nd part of the jig.
434
19) Note the invisible support placed manually between the indexer aluminum rail and the underside of the jig.
435
20) Remove the cylindrical peg we used to load the part in the jaws of the indexer jig.
436
21) Machine the sixth face.
437
22) Close the jig...if the model requires more than one cutter we’ll have to do more work – and we’ve already cut off our cylindrical peg! Looks like we’ll have had to organise our cutting “per cutter” for faces one to five together, and then “per cutter” for the sixth face after the “hand-over” to the 2nd part of the jig.
438
23) Remove the finished part
439
24) Leave everything and go and make a cup of tea. Then start measuring to find out if its within tolerance and visually inspect it to find out if you’ll be able to hide the imperfections by hand-finishing.