Hopeless…Alibre Ass

[blowlampParticipant @blowlamp]

Nigel.

“I deleted both drawings and re-drew the cover. That was easy but I have not created a new model for the crosshead body. That could take me at least three hours, thanks to its fancy shape needing a lot of geometrical construction.”

Is there any chance of you posting a rough sketch of this part and I’ll try to show you how it could be done by Direct Modeling?

 

Martin.

[JasonBModerator @jasonb]

He can’t produce reliable parts at the moment so whatever he chooses is going to be a challenge. If he is using one unreliable part to directly produce mating ones then they will both have errors. At least doing separate parts there is a chance of the errors being flagged up when he tries to assemble them.

 

 

 

 

 

 

 

[JasonBModerator @jasonb]

Middle of the cross head is similar to this

Side plate a bit like this

Same plate on the other side to complete

I used the ctr part to base the side plates on onlt needing to enter the diameter of one larger clearance hole and the amount the plate protrudes at the top and its thickness. all other features related to the ctr and will change with it. It also includes the deliberate error that carries from one to the other.

[JasonBModerator @jasonb]

This thread was the previous time we tried to sort out Nigel’s crosshead. Though it is now a 3 piece as post above

[Nigel Graham 2Participant @nigelgraham2]

I tried to edit the drawing but without success.

I managed to change one dimension but not the other, and that on just a rectangular plate with a rectangle of holes for screws.

The crosshead body is much more complicated, and the faults were the width of a recess and the layout of the corresponding screw-holes.

I had already made the real components but mis-measured them for drawing them so I can design their surroundings.

 

I may as well say, “To Hell with formal drawings”, and just use those already done as literal “3D models” plus rough pencil sketches on the backs of the ME&W magazine address-sheets. As I have with some components already.

 

Videos are very variable. Paul Tracey recently sent me very good ones he’d made for TurboCAD.

(TurboCAD’s manufacturer, IMSI, has contracted making tutorial videos to another company. I viewed them but it was obvious the contractor simply publishes a few random ones from three separate series. They are presented very well, but do not transmit to their full lengths [file-size limits?], and the overall result is poor. My impression is that the contractor is purely a third-party technical publisher who does not fully understand the subjects, and with poor oversight from IMSI. IMSI itself now belongs to some outfit not necessarily CAD specialists.)

I did also study the introductory material for Alibre, used in its MEW series.

Generally though, I had been put off a long time ago by “tutorial” videos that were hard to follow; more demonstrations of expertise than instructive.

Also, I find a static manual, printed or in .pdf form, far easier to use than moving pictures anyway.

 

While I am very grateful for all help, I don’t want to rely on deeper informal tuition gambling other people’s valuable time on my abilities. Allegedly I once had an unusually high IQ (by NHS record… even the experts can make mistakes!); but I know I was always a very slow learner with unpredictable but low natural limits for any subject. CAD is no exception, and not alone.

 

I don’t want to adopt yet another CAD system I could no more learn to its full advantage, than TurboCAD Deluxe or Alibre Atom.

Those two differ considerably, and each has its own strengths, limits and level of difficulty quite different from its rival’s. Although I can overlap them enough to be useful, that is not ideal.

If I could, I would use just whichever is the one easier for me, for both single items and assembly drawings.

 

[Nigel Graham 2Participant @nigelgraham2]

Having just seen Jason’s comment above about “unreliable parts”…

There is nothing wrong with the physical cross-heads I made! 

I like his suggested way to make them but I used a pair of castings from the waifs-and-strays tray on M.J. Engineering’s trade-stand. They may originally have been for a 7.25″ g. locomotive, by their shape and being a pair cast in one.

My dimension errors were in the drawings I made of them later, in their finished form. Not on the actual metalwork.

Though I now realise the mistakes would have stopped constraining them together as CAD parts.

 

I have to replace real parts already made far more to improve the design or correct design flaws, than to correct simple metalworking errors.

I had hoped that using CAD would help me design the lot before using up any metal; but no. All it gives me is much quicker and intrinsically more accurate drawing, and easier editing, than by hand. My dimension or shape mistakes on a drawing are nothing to do with how I drew it.

Editing… Well all right, replacing the drawing if I can’t alter it. Which I usually can’t.

Modifying the faulty cross-head body model might have been possible but certainly not easy, and anyway I assumed it useless and deleted it. A copy does exist on a partial assembly and might be salvageable from that. Which makes me wonder if in fact I re-draw the thing at some point, and put the mistakes in the second drawing.

[JasonBModerator @jasonb]

I meant you can’t produce reliable CAD parts. So using one to drive the design of another would just give two parts with errors.

The part file should still be in your recycle bin and can be retrieved from that.

[Nigel Graham 2Participant @nigelgraham2]

Ah, I’d not done it like that.

I’d measured one piece of metal and drawn that. Then I measured the other bit of metal and drew that one.

Only, I’d mis-measured both so both drawings were wrong, and their errors differed. The real bits of metal fit together but the images of them don’t because their mating features differ!

No wonder none of the constraints would work, but that was not obvious to me for a long time.

….

I did try using Alibre again this evening but for something else completely. I have just fitted my Harrison lathe with a boring-table and need make adaptors to use existing tool-posts etc. I needed widen my first sketch of the upper plate, a preliminary design for holding the lathe’s original top-slide (albeit with a big loss of tool height). I still can’t edit a drawing’s dimensions though so had to re-draw it, even though it is just a rectangle with some holes in it. I doubt I created the Tee-slots in the best way either, plotting the initial profile for each, individually. Nor could I work out which planes to use for for the best so the table was the right way up but I had to turn the plate round in two planes. The engraved “F” (front) is not on the real thing. It’s to orientate the drawings.

 

 

 

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