Real world v SolidWorks 1

[charliedurrant]

Bare with me everyone, I know I'm as king a lot of questions....(and thanks to all that have taken the time to answer so far)

Background - I am new to modelling / CAD / drawing etc. I am transferring some old autocad files into a 3d model. The files represent a replica of an old swing frame - nothing smart, just some tubes, hinges and an apex joint.

The whole lot is at

http://www.wilverley.com/Assembly.zip

and the the e-Drawings file is at

http://www.wilverley.com/Assembly.htm

I have two problems:

1) I have a folding brace (like the ones you get on baby push chairs) which connects to tubes which are fixed at one end to a joint. The brace locks the two tubes (legs) and when locked out fixes the distance of the two legs.

The problem is in 'the real world' the brace has an element of flex around the set screws where it is fixed and both faces of the stay that connect to the legs sit flush against the legs. Solidworks wont let me create a coincident mate as this would mean the other components would have to twist. It makes sense ofcourse but in the real world I am not forced to have a 5mm gap..... What should I do to emulate real life.

2) Before the legs were linked together by the brace they had movement in two ways

a - rotation about the set screw where they are fixed to the apex joint hinge.
b - where they are attached to the apex joint, the hinge they are attached to had perperdicular rotation about another set screw.

Once the two legs were linked by the stay I lost movement 'a' even if both legs were selected together.

Thats the end of my questions ! I can't find anything in the help files or on web searches etc.


Charles

 

[SnowCrash]

Or maybe I misunderstand you. Do you meen the flattened part of the tube. It is a seperate part, but how do you mean to constrain it lige a hinge? Charles

Yeah, I meant the flattened part of the tube could be a separate part. Constrain it to the tube with centerline plane to centerline, then one edge to the surface of the end of the tube. This would allow it to flex the way it actually does bend.
"Sort of"

--
Hardie "Crashj" Johnson
SW 2005 SP 4.0 (reluctant to change)
Nvidia Quadro FX 1000
AMD Athalon 1.8 GHz 2 Gig RAM

 

[charliedurrant]

CorBlimeyLimey,

Thanks for info re the ball joint. I have now made the legs parallel by aligning the sides of the parts that join the loft - they were parallel and were parrallel as enforced by the stay before hand.

Still no luck - this is all very strange and I still can't see why the legs don't rotate with each other. If the hinged stay flexes with the movement of a leg then why don't the two legs rotate with each other since the stay is locking them together. The rotation does not pull the stay out of is mated position......Going very mad now...

For what it is worth I have updated

http://www.wilverley.com/Assembly.zip

'Assembly - Side' being the main file.

Charles



Charles

 

[charliedurrant]

SnowCrash,

But the tube doesn't actually bend in real life it rotates around the set screw that connects to the apex joint. This is hard to describe in words and I again could be misunderstanding you.

The tube can also go 'in and out' perpendicular to the rotation as the thing it attaches to is a hinge (of sorts).

I am very much a novice and I hope I'm not getting the wrong end of the stick and I do appreciate all comments made.

Charles

 

[charliedurrant]

I'm wondering if this is a bug in Solidworks. I'm continuing to try but logically Solidworks should understand the model.....

 

[smcadman]

It is not possible to fold the legs because of the concentric mates on the legs and brace. You would need a universal joint for the hinges to bend the legs back in SW. You might be able to cheat that effect by adding a point to the holes and constraining the points to the temporary axis of the mating holes. Also add distant mates to the points.

It isn't a bug in SW, the only reason you can fold the legs back in real life is because of the gap between the screw holes and the screws.

Flores
SW06 SP4.1

 

[charliedurrant]

Flores,

Are you saying that 0.2mm gap between the set screws and the holes which in real life is much less due to paint is allowing the legs to rotate around the hinges by 180 degrees?

I have a frame in front of me and the bolts you mention are torqued to a good amount and there is probably only 0.1 mm diameter difference between the bolts and the holes and probably less as some needed to be twisted throught the holes due to thick paint.

If both legs rotate around the the point where they are fixed to the apex joint (at the same time and with each other) how can the concentric mate be broken?

I can understand one leg can not move without the other as the concentric mates will be broken but both at the same time is fine. I'm not trying to labour the point but I just don't see why the legs can not rotate with each other around their respective apex fixing points.

Charles

 

[smcadman]

I went upstream to the Assembly Apex Joint, and one of the problems is there. Mater errors, not SW bug. In order for the legs to fold forward the 2 parts "Hinge" would have to be parallel to each other. Open Assembly Apex Joint.SLDASM and pick the 2 holes highlighted in the screenshot below; you end up with mate errors.

http://img412.imageshack.us/my.php?image=assemblyapexjointvv3.jpg

There isn't a fudge factor in SW, I don't know how many decimal places SW is accurate to, but if your holes are off by .0001, your concentric mates and other will cause errors. In real life, there is wiggle room.


I will say that I think you are the first one that I recall using eDrawings instead of static pictures to help us help you.

Flores
SW06 SP4.1

 

[charliedurrant]

Flores,

Are you saying I should be able to make those two holes concentric? I should and I can't, suggesting there is a problem. The problem must be in holes of the front back plates of the joint...... Checking it all now - v. embarassing if it is......

Charles

 

[charliedurrant]

Flores,

I think you may have hit the nail on the head so to speak. I think it is definately 'Apex Cover Back Plate' that is causing the problem and apex cover front plate is derived from it by hiding / showing an extruded cut.

I have modelled the back plate based on the profile of the 'Apex Cover Formed Plate'. I have used the formed plate in terms of looking at the measurements / dimensions.

The arc was wrong and the profile just out when precision was increased. So..... can I make the back plate using the exact profile of the formed plate using some tool method that is outside of my knowledge. If there was such a way I would know the 'back plate' would always match the 'formed plate'.........the legs may then move and that would be a relief......!

Charles

 

[charliedurrant]

p.s. I know it must be the left and right hand set of holes of the front and back plates that are out of align but I should fix this problem first and irradicate all errors ....

 

[charliedurrant]

Flores,

Still no joy. The holes on the hinges as indicated in your picture can now be made concentric. There is still no circular movement around the bolts that attach the legs to the apex joint.

Is there a way to define that two parts should always move together.... This is what I see as the problem. If both legs moved together then all would be OK. In my tiny mind this just doesn't add up.....

The later stages of the assembly require that the legs can rotate with each other as the 'A frame' is braced to a central beam.

Without movement at the joints indicated as it stands SW can't model what I have standing next to me

Assembly reposted to

http://www.wilverley.com/assembly.zip

with the main file being 'Assembly - Side'

and eDrawings file posted to

http://www.wilverley.com/assembly.htm

Charles

 

[SBaugh]

IN SP4.1 I get a bunch of errors because you have over mated the assembly.

1) forget about the bolts and screws and just mate the assembly the way you want it to work.
2) make sure the assembly is working after each mate.
3) as you add the bolts continue to check the movement after each one. this will help you determine which mate is causing the problem.
4) The Parallel mate (legs) seems to be one of the mate issues, along with to many coincident mates.
5) I suppressed all the bolts, washers (except those that separate the legs) and deleted all the mates and started over.
6) You could make 2 configurations setting up each one to do one operation. You won't get this assembly to move in both directions with what you have on this assembly.
7) with a config you can suppress and unsuppress what mates you want to have activated. This gives yo uthe advantage to determine what's on and whats not.

but as to moving in both directions no I don't think is going to be possible, not only because of the Parallel mate, but also because ofhte hinge at the middle of the legs. They also control location of the legs. COnfigurations maybe the only thing you can do or maybe write some equations.

Regards,


Scott Baugh, CSWP

http://www.scottjbaugh.com

faq731-376

 

[charliedurrant]

Scott,

Thanks for having a look. I'm running a second hand copy of SP0 and I have no errors. Also the parallel mate is not really required as the other mates infer the hinges being parallel.

So I'm left with two seperate configs.... Am I just imagining it or should it really be able ro have both type of movement. If I delete the parallel mate nothing is any better.

I'll do as you say and essentially start again however its difficult as only once the legs are attached in all the places shown does it all go down hill.....I hope not to beaten by this !

Charles

 

[SBaugh]

I am using SP4.1 so it could be the SP you and I are on. I didn't delete them I just suppressed all the mates. It's very confusing that's why I suppressed the bolts and stuff to bring it back down to the basics. try getting to the basics and see what you can do there.

Regards,

Scott Baugh, CSWP

http://www.scottjbaugh.com

faq731-376