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How to find the scale of a beam in the beam custom feature?

gerald_comeaugerald_comeau Member Posts: 61 ✭✭
I am still taking Learning Onshape courses but also beginning to experiment to see if I can put what I have learned into practice. I have been practicing with the custom beam feature after watching the weldments webinar.  I arranged a Wide Flange Beam in a circular pattern to make a carousel platform. The scale I use for the circle is 1mm:12.5mm. 
I started with an arc of 400mm radius (400mm:5000mm) and used 5 units of the arc to circle the beam. The circle scale and the beam  scale are incompatible. I don't know how to fix this or where I went wrong. Here is the document:   
https://cad.onshape.com/documents/b0035e05f853ec87e70c483a/w/e989a161cfa5c90af1778a46/e/7aa7f91b616cf313c39330f1 I knew the scale issue would arise from watching the webinar but went ahead anyway to practice and to illustrate my problem. 

To digress, here is a beam I extruded before finding out about the beam feature. The exercise was a failure but it illustrates roughly the relationship in size between the radius of the carousel and the beam. 

Background: My ambition is to innovate in concentrating solar power. The concept is to use a transparent convex flat lens of the Fresnel type. This lens will direct the sun beam downward to the ground instead of upward toward the sky, as in the case of a parabolic dish. There are significant advantages to directing the beam toward the ground. Capability for heat storage is just one of those advantages. The concept has been attempted in a pilot project, but I don't see any sign that it has gone into production. Here is a 4:35 minute video of that pilot solar power plant. https://www.youtube.com/watch?v=3oN1nh-XWVo&list=PLwCY0cZvkCFFOKYhvBEGWC5gHYktyJhim&index=2&t=0s  My concept is very similar but its execution is quite different. My aim is to make a more rugged structure. Also, my goal is to have all the parts of the parts fit into a 40 foot container for shipment and easy assembly at destination. 

Best Answers


  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 2,391
    edited June 7
    Hi @gerald_comeau - I'm not really sure what you are asking? First, why scale? You should model everything at 1:1. For the beam size, you can create your own beam profile as a sketch (then use the custom option in the beam feature).

    Note that all custom profile sketches must be sketched on the Top Plane.
    Neil Cooke, Director of Technical Marketing, Onshape Inc.
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    to Neil Cooke and Chris Bower, I have sketched the end view of a W-Beam and I have no difficulty doing that 1:1 but what good is that to me until I've extruded it. That's where I've run into difficulty. Once I made a profile of the end view of the beam 1:1, at about the size shown in the beam feature, I ran into problems with extrusion. I attempted to extrude an arc which makes 1/5 of the circle with the sweep feature and didn't get a smooth arc. Even 1/5 of the circle made a very long arc. To make a long story short I could not succeed in making an arc from the end view of my sketch after having tried different features. Perhaps this was because of my inexperience or maybe I am just too clumsy :). I am happy I've made the discovery of the beam custom feature. I have now successfully used it to make an arc to a 72 degree angle, which is perfect for what I need. That has been my goal for the development of the carousel. 

    Chris Bowers indicated scaling in drawings. My plan was to make more parts before going there. If I understand you correctly, I'm at that stage now.  The challenge now is to use the arc that I've already made and proceed to make parts which fasten the beams together. I should mention here that I intend to do as little welding as possible on this project because the finished product may end up in destinations where there is little industrial infrastructure. For this reason I need to make plates for bolts in the shape of the arc and use these to fasten the beams together. This takes me to sketches. I want to make sketches that will fit. I know the dimensions, but I am not sure if I understand how to arrive at the size of sketch plane I will need. From the webinar, I believe the instructor started the sketch with a rectangle of 1000mm X 750mm, (I'd have to look it up to make sure.)  I used a sketch of 1500mm X 1500mm to make the arc so I can use that. Am I right? 

    Thanks guys. 
  • Cris_BowersCris_Bowers Member Posts: 281 PRO
    I don't think you are at the drawing stage yet. You will want to get all your parts modeled before you go there.
    I took a look at your model sketch and I'm not sure what the purpose of the 1500x1500 rectangle is, unless it's just a check to make sure you stay within that footprint. Unfortunately I have some work I need to get wrapped up today before I leave for vacation so I'm not going to be able to be much more help for the next week. Sounds like a neat project though. Good luck.
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    Thanks for writing back. You've confirmed my thoughts on modeling parts before going to drawings. I'm not sure myself why I made the 1500mm X 1500mm square. I was just following what the instructor of the Weldmans Webinar. (Somehow his name has disappeared). I asked myself the same question as you when he did it. It ought to hold me within the "footprint" though. 
    Enjoy your vacation and get rested up for the hard questions I'll come up with. 
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    Neil Cooke, I wrote back to you as you may have already seen. I added a comment at the end of my message on the helpfulness of your reply but it seems to have disappeared. I didn't know how to reply because in a sense it was helpful and in another I was still unsure on how to proceed, so I checked "no."  I did appreciate your reply though and in the end it became helpful as I worked through my own thoughts. Thanks.   
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    john mcclary, ....lean and mean CADdies. That's a great list of tips: and 10 of them too. Trying to be a GOOD student, I have already recognized some of these tips through practice and observation and am working on being mindful of them. I'll be keeping this list for quick reference. Thank-you. 
    I've got to admit though, I am a little puzzled by the term "model full scale." I've of thought of a scale as always full ....like a map, so many (x) mm to (x) km. It's not possible to squeeze in an additional town from outside the confines of the map ....or try to increase the size of a county without changing its borders, to make room for farmland from outside its borders. That would not be true to scale. In CAD you can blow up or reduce the size of the sketch plane while remaining true to scale, but as in the map you can't squeeze in another beam when there's already a beam there.
    There is one thing in Onshape that I don't yet understand. I've noticed that the planar faces are not always in direct relation to the size of the sketch plane or vice versa, as if they're independent of each other. Am I right or am I confused? I'll be relieved once I understand this fully. I've looked and searched for explanations for this and so far have not found anything. I'd be grateful if you could point me to information that would solve this mystery for me.   
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    To John McClary and Neil Cooke -
    John, I like "We don't scale, we zoom." ....also good guidelines on the usefullness of scale in models. 

    Neil, so that was you in the weldments webinar. I did not recognize your voice.  I thought the audio was better than usual. Did I detect a slight British accent. I have a french accent. The building of the frame of the gocart was dazzling. I thought the square pipes were OK but the the round pipes looked a little flimsy. Would you mind replacing those with W-200 beams? ...just kidding. See. I'm learning. 
    Serioulsy though, you guys were a big help to me in getting over some hurdles. Many thanks. I have to remind myself that we are in cyber times. We can move Nova Scotia to the Gulf of Mexico with Photoshop in the blink of an eye. We can create Russia conspiracy theories on youtube, we can have a wallet with invisible coins in it and we can make great models, gocarts for example, on Onshape, We could become schizophrenic.  What a wonderful woild. 
  • gerald_comeaugerald_comeau Member Posts: 61 ✭✭
    Neil Cooke - You wrote: "Am I right in thinking that your 1500mm^2 sketch was your interpretation of sketch planes and scale? A plane is infinitely big and has nothing to do with the size of your sketch. Keep practising - it will click."

    I meant to answer your question but got distracted by something else and forgot. The whole notion of sketch planes and scale were a little foggy in my head and I had no firm idea.  I did realize immediately though, what happened  when in your Weldments Webinar, you drew the "skeleton" sketch and placed the beam on the edge of it. So I understood that much. I have always zoomed in and out until now by using my mouse wheel but your skeleton sketch showed me another way it can be done. The fog is clearing and the biggest lesson I've learned is always model 1:1.  Thanks for the encouraging comment that it comes with practice.   
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