All parts except for the turned parts were done by waterjet cueng, bending and
spot welding. Total fabricaâon âme .... Ma. Dies are cut into different lengths to
allow complex bends ... with the same equipment ..... for homemade plain
How to make things! Robin Coope Props to Dan Gelbart, Jon Nakane, Bernhard Zender, Juga Kitanovic, Charles Guan, Alexander Slocum and Google Image Search
I am an Engineer! Why Should I Personally Know How to Make Stuff?!
You should know how to make stuff because! • You will get your prototype parts much faster! • You will be able to iterate your designs much faster! • Your designs will become much more efficient as you understand the cost of each process. !
Whatʼs the big deal about waterjets?! • It is by far the easiest and safest computerized machine tool available.! – Students can actually use it!!
• It can cut a very wide range of materials! • Itʼs much faster to waterjet small part runs than any other machining method.!
A Prototype Medical Tool
All parts except for the turned parts were done by waterjet cuJng, bending and spot welding. Total fabricaLon Lme ~ 8 hours. Dan Gelbart
The GSC Size SelecLon Robot
All non OEM parts except acrylic plates are water jet.
CT Test Jig. 90% Waterjet All carbon ﬁber cross secLon for CT scanning
Seth Gilchrest UBC Centre for Hip Health
CT Test Jig. 90% Waterjet
Re-‐designed to maximize water jet-‐only fabricaLon with only a few threaded holes added aZer
A Dryer for a 600 ppm Inkjet
All parts of both dryer and control are WJ, bent and welded. No other machining Dryer is doubled walled with dual air bearing heat transfer. Dan Gelbart
What is a Waterjet?
A waterjet is a “ﬂoppy grinding tool” not a cuJng tool. Sand and water in a 1” Aluminum. Use it to your advantage
Jared Slobodan BCGSC
Causes of Bad CuJng WATERJET
YOU’RE DOING IT WRONG
Andrew Porrit, UBC Mech
• Poor sand feed – check for parLal blockages • Bad Nozzle – should last >50 hours. • Part vibraLon – bejer clamping or tabs needed
The Good and The Chipped Note opposite facing waterjet marks on two halves
Maj Lam UBC Physics
• Speed drops as thickness1.15. • The pracLcal limit for Aluminum is ~2” • It can be faster to stack thin parts to ½”. • Advantage vs. milling greater with hard and tough materials.
Working with Sheet
Metal and PlasLcs Come in Several Forms • • • •
Plate (1/8” and thicker ) Bar and tube (round, square) Extrusions (complex shapes) Sheet (thinner than 1/8”)
Sheet Materials • Typical sizes
– 12ga (2.5mm), -‐ structural elements – 16 ga (1.5mm) -‐ Structural, motor mounts – 20 ga 1mm, -‐ Enclosures – 24ga .7mm .025” – 253 Robots!
• CR means cold rolled mild steel. Stainless is 5x more expensive • Shim stock (301 Half Hard) is a hard spring steel. • In Al, can get 6061 T-‐6 and 5052. Only 5052 can be bent. Gauge sizes are slightly diﬀerent between aluminum and steel.
Comparison of bent and mulLpart components
2 diﬀerent pieces of plate must be cut out Drilling and tapping on the mill is required
One piece of 12 ga cold rolled steel or 5052 aluminum Harder to get the 90 angle just right Not as sLﬀ
Comparison of bent and mulLpart components
Machined aluminum dishwasher rack at leZ was >4x the cost of the WJ stainless version, and harder to use and prone to corrosion.
Guides from CNC back gauge
Top die Maj
There are two lower dies, .75” and .375”. The smaller die is bejer for 24 to 18ga. The gauge ﬁngers can get in close enough to bend ~ 8mm ﬂanges with the small die, 14mm with the large. A12 ton press brake can bend > 120cm @ 1mm and ~ 30cm @ 2.5mm for steel
Dies are cut into diﬀerent lengths to allow complex bends
Sheet Metal Rules
Complementary Errors! • The posiLonal uncertainty in these bends cancel each other out as everything is bent at the same Lme with the same equipment
Box Aspect RaLo • For most bends the height of the ﬂanges must be less than the width of the box • PHAS has a “dog leg bender which allows higher ﬂanges on smaller ¼” and Lghtened into nuts.
Machine screws: Lower grade than cap-‐screws, cheaper, driven by screwdrivers Stud: Welded onto or through a surface. Requires a nut.
Shoulder screw: Has a bearing shaZ Lag Screw for wood. >1/4”
Self tapping screw for thin sheet metal 0.005”! • Bearings need +0.001”, -0.000”. Use a reamer to make very accurate holes! • For bearing systems use shaft rod and not drill rod! – “Drill rod” is ± 0.0005, “Shaft” will be +0, -0.0005”. ! – Drill rod and some shaft is also hardened and canʼt be machined. !
Transmissions • ShaZ posiLons should be laid out according to theoreLcal gear diameters • ShaZs should only be supported at 2 points – use ﬂexible couplings as needed – eg servo potenLometer • SupporLng either side of gears is much easier. • ShaZ clamps should be used to prevent axial translaLon
Plate and Standoﬀ
Make the transmission on the waterjet except…
Source: Charles Guan, MIT
Bearings ! Plain Bearings (bushings) Ball Bearing
Flanged Ball Bearing
• Ball bearings are low fricLon but more expensive and tricky to install • For the climber bots, plain bearings will probably be ﬁne. • Steel on steel is OK but may bind under higher loads. Al-‐ on-‐al = bad! • Polyethylene (poor man’s Teﬂon) is a good material for homemade plain bearings.
Linear Motion! • This drawing shows the key features which any linear moLon must reproduce in whole or in part. • The hardest thing to make cheaply is are the linear guides and followers themselves. • Following are some low cost ideas
Linear Motion! • “Ready Rod” threaded rod is available from 4-40 to ¼-20 in stores! • “Chase” with a threading die to clean! • The follower can be made from solid teflon. Make thread length 2 to 3x diameter!
Linear MoLon • Drawer slides are one cheap but heavy source of linear moLon. • For 253, solid plasLc sliders on metal tubes will work if ﬁts are loose and loads are low. • For bearings, couple shaZ directly and only use one bearing at the far end of the lead screw.
Clamping to ShaZs Splines. Great torque resistance. Can be end-‐bolted if the spline is tapered or split bolted (e.g. Futaba servo output). A loose ﬁt will “nag” the splines and wreck the shaZ. Can also be used for longditudinal sliding torque transfer. Woodruﬀ keys: A single slot for a steel shaZ and hub. Material of the key (e.g. brass) is chosen so it can break under a speciﬁed load, as a safety mechanism. A waterjejed crank and counterweight with woodruﬀ slot
Clamping to ShaZs ShaZ collar
Set Screws and collars PosiLves: Easy to make, can use on any shaZ. NegaLves: Can mar the shaZ, not much torque resistance, easy to strip small set screws, need to use shaZ ﬂats for bejer grip larger shaZs. Best used with small shaZs – eg Physics 253 robots!
Coupler with two diﬀerent shaZ diameters. 8-‐32 set screws are much stronger than 4-‐40’s
The best shaZ and bearing connecLons Step 1. Waterjet with main holes undersized by about .025”. Powdercoat at this point too.
The best shaZ and bearing connecLons A Reamer
Final Size .375”
Final Size .875” Step 2. Ream holes to exact size
The best shaZ and bearing connecLons
Step 3. Drill Clear holes. Drill and tap lower holes.
The best shaZ and bearing connecLons
Step 4. Remove tabs with a hacksaw
Assembled Crank Arm ShaZ
Resistance to torque at the shaZ and axial load at the shaZ and bearings will be very good.
• OMAX layout is great for gears • Teeth/Pitch = Diameter • Use a pitch > 24 for waterjet • Run gears back to back to match tapers • Can drill set screws through the gear body
Flexure • Can be made from solid stock (aluminum, niLnol plasLc) or welded together. • Best ﬂexure material is 301 half Maj hard stainless ~0.005” • For fast moving parts, ﬂaring the sLﬀening plates is criLcal to prevent faLgue failure.
High Density Polyethylene Or Delrin
A mounLng system for two Wiring boards which allow the boards to be removed without tools
The Adiabatmobile, Physics 253 2010
Post Paint Machining
These aluminum hard drive bodies were die cast, painted, then machined in key spots. This is the way to rapidly make precise parts.
A Lesson From Professor Alldrij Unlike code or electronics, mechanical parts are visible. By just looking, you can appreciate the genius, or folly, the craZsmanship or sloppiness of manufactured items everywhere. Pay ajenLon to how things are made; you will be a bejer designer.