In this Fixturing Fundamentals episode, Jason continues to fabricate parts for building out the Sci-Fi office, this time focusing on the complex railing. Leave all your questions and comments here, and let’s discuss it!
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It can be viewed on the website exclusive videos page prior to our YouTube debut
Are the spacer blocks made from a ferrous material? If so would it be ok to use a magnet inside the detent to stick spacer blocks to the fixture pin drop-ins?
What a great video! I learned so much. But full disclosure I’m not a welder nor do I have any ability to fabricate anything out of metal and I do not own a fixture table or a CNC router. However I’m a big fan of 3D printing, I also own a small but good laser printer and I sometimes make things out of wood. I’m also quite handy with CAD. Watching this video inspired me to make mental notes of some potential (but hackier) ways that could help me make identical pieces out of wood. 1) I could 3D print some fixtures that could be clamped down or screwed down. Could use wood but it’s easier and quicker for me to 3D print and control the accuracy of 3D prints. 2) I could laser print some full size drawings to get layout on paper. 3) I could use a grid pattern to make sure my small A4 size drawings align with each other when making bigger things.
However I found in the past that printing larger pictures as tiles accurately with a small printer can be challenging. Does anyone have good techniques for calibrating, tiling, printing larger drawings to get accurate results for layouts?
From the video it also looked like if you CNC routed a bigger template you could have placed fixtures against it pretty accurately. Any CNC templates could probably use round clearance holes at all corners to not interfere with bend radiuses.
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Considering the 2nd method, wouldn’t it be possible to etch/laser/cast these alpha-numeric hole designations into the final product already? That would be a great help, or maybe add it as a paid option before check-out.
Yes future tables will have the grid labeled. We’re also working with other table manufacturers to make this grid a standard on all fixture tables.
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The end result with the initial layout done in cad is obviously better, and probably faster overall, but it would be interesting to see the time difference INCLUDING laying out the blocks in CAD, especially if thats done by an engineer instead of the fabricator, because those are going to be additional billable hours. Additionally, might take them longer because they probably won’t be familiar with your fixture table, so unless you stick with one engineer, you’ll have to pay for them to figure it out every time.
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All of our fixtures are steel and our shims that we were using in the video except the 1/8" and smaller are magnetic to they can stack on each other or attach to fixtures.
It took me about 8 minutes to lay the part and fixtures out in a Solidworks assembly and make the print.
Are the Cad models of the tooling and table available? I would say without access, method #2 would be tough to execute. Other than spending a few days, depending on skill level to model everything.
Most of the fixtures are simple shapes like blocks and rectangles with holes. It shouldn’t take long to draw the fixtures that you have.
Raises an interesting point about desisning for production. For a stochastically oddly shaped part (as opposed to one where its odd shape is intrinsic to its correct function or for a precise structural reason) it makes no sense to not design for the grid rather than just on the grid. Most obviously to me this means picking angles that make Pythagorean triples or otherwise meet the tangents of the grid holes such that fixturing can be done simply with two round pins.
Of course this assumes you are both engineer and fabricator, but some simple corrdination with your fabricator might mean thousands saved in outsourcing costs even for small firms.
It is hard to emphasize this strongly enough!! Designers should know what their fabricators can do and fabricators should ask designers questions till they understand design intent (Then get it in writing or in drawing revisions!)
Discussion was invited. I hope this doesn’t come off as too critical:
It is also incomplete (But I don’t think the weld/assembly video made it all the way to the end either) If there is any enthusiasm for it I’d go on (and on, and on…)
- The only drawing I saw was titled “Fixture Table Layout” or something of the sort. It appeared to be a representation of the final result, without respect to which segments were provided by which components. (As if the result was to be 3D printed, extruded, or carved from a billet?)
a. Are there any drawings of the parts being welded?
b. Are there dimensions and tolerances for the components?
c. Is there a drawing of the weldment indicating assembly dimensions/tolerances and weld locations/specs? - Was there any inspection/measurement of the bent flat-bar components? They were stacked together, affording a comparison that would have revealed variation within the batch, or a single part bent wrong, but not all of them bent consistently, but wrong.
- There are two distinct things that weld fixturing does: 1) Hold parts in a specific relationship to each other throughout the welding process, and 2) Hold multiple sets of components as close to exactly the same for each weldment made. Some setups favor one, and some the other. Both should be recognized. We’re making thirteen(?) of these things after all.
- Each detail part, assuming it is formed correctly, must be located in a specific location relative to the other parts placed in the fixture. It is BEST PRACTICE TO NOT FLEX ANY PART by force applied using the fixture. And if a bend line is less-than-perpendicular across the flat bar? It’s best to know now, rather than when welding…
- To locate each component part, six degrees of freedom (DOF) must be restrained: Up/Down (U/D), Fore/Aft (F/A), and Left/Right (L/R) translations and then rotations around each axis (U/D), (F/A), and (L/R). Three translations and three rotations. If any degree of freedom is un-restrained the component can slide or spin (and “slightly” is too much motion).
- To locate a component without flexing it it is important to NOT over-constrain it. The most common way this is thought of is often referred to as the “3-2-1 Rule”. A part sits on 3 points on the table, is pushed back against 2 points on the back gage, and is slid against 1 point on an end stop. 3-2-1. Coincidentally, and sometimes confusingly, the count of DOFs thus restrained is also 3-2-1. The table stops translation U/D, rotation around L/R, and rotation around F/A. The back gage stops translation F/A and rotation around U/D. The end stop stops translation L/R. That’s six.
- If I’m not mistaken, these are the parts:
a. Part #1 (Long piece with 2 bends)
b. Part #2 (Short piece with 2 bends)
c. Part #3 (Small piece with 4 Holes)
d. Part #4 (Small Bent End Piece)
e. Part #5 (Small Flat Gusset) - All the parts seem to be made from the same stock. The stock dimensions are controlled by “Mill Tolerances” for flatness, thickness, and width. Each part is made from a cut length with a tolerance CHOSEN BY THE FABRICATOR or the customer.
- Some evaluation of the flatness, thickness, and width is inherent in selecting “good” material. I have found it surprising how much variability mill tolerances actually allow. This can actually become problematic when one becomes accustomed to material having less variation and then is provided with material that barely meets the mill spec,
- It looks like some of the long parts are being fixtured with, in effect, 2 end stops. Unless the bend(s) is (are) perfect, either one stop won’t touch or we’ll be flexing a bad(?) part to make it touch. Not a good practice.
Jason: while setting up and recording method #2 for the very first time, if you failed to say the words out loud “you sank my battleship” then you have to turn in your Nerd Card right now.