Fabrication Techniques & Hardware

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A milling machine has the limitation of using a round bit, which means that many traditional techniques of joinery cannot readily be made (but see below). There are also a number of fasteners and other sorts of hardware, many of which are made possible by modern technology and metallurgy and in their newness are somewhat obscure. This page is intended as a collection of such techniques and hardware, w/ links to actual implementations and usages.

See also Designing for Fabrication for a more in-depth discussion. Note that some references on the Materials page contain engineering data and standards.

Tolerances

Any instance of one part fitting to another will require that one work out the appropriate tolerances for the fit.

http://www.engineersedge.com/general_tolerances.htm

Discussion of measuring various hole tolerances: https://www.reddit.com/r/CNC/comments/6bwhtu/what_does_a_machinist_do_differently_when/

Joinery

There are many different techniques for making joints --- woodworking in particular has an old tradition of them, but many traditional joints are not readily made on a machine w/ only 3 axes using a rotating bit. The flexibility and control which CNC affords has however created the possibility of new classes of joints as noted below in Other Joints.

One may wish to use a jig to hold a part for cutting as was done in these Dowel Holders which were used in an elegant Plant Stand.

http://mkmra2.blogspot.com/2014/08/cnc-cut-wood-joinery.html

There are specialty software options for joints such as JointSCAD for OpenSCAD.

Interlocking part tolerance

MDF required about 0.015 inches (~0.381mm) clearance[1]

Rabbets

  • Double and blind rabbets are used in this wooden box.

Drawers

http://imgur.com/gallery/2tjZ0/new?forcedesktop=1

Dovetails

It should be easier to cut full-blind joints by using a jig which holds the two pieces to be joined at 45 degree angles to the mill.

Normal dovetails can be cut using a jig which holds two pieces of wood vertically at the front of the machine using an endmill and dovetail bit.

See https://www.shapeoko.com/wiki/index.php/Commercial_Software#Joints for commercial software for this.

Knapp Joints

Invented by Charles Knapp, sometimes referred to as a pin and scallop. It was the first machined drawer joint (produced from ~1870 to ~1900).[2]

Mortice and Tenon

Cutting mortices and tenons is complicated by using a round endmill to cut what is traditionally a rectangular pair of features --- another consideration is how the parts are presented to the machine --- if a rounded tenon is an option (the part with the tenon is presented to the machine vertically for cutting), then the parts will simply fit, so long as the endmill geometry allows this.

For the other cases, there are a couple of different options:

  • dogbones --- for large-scale parts, or when using a small endmill, this is a viable option:
Dogbones.png

Draw a circle equal to the endmill diameter + 10%, rotate it 45 degrees and then align a node against a corner. The illustration shows an instance where the part is too small / endmill too large for dogbones to be feasible.

  • reshape the tenon

Dimensions and proportions: http://woodworkstuff.net/KnipMT.html

Floating Tenons

Other Joints

A great resource is the "50 Digital Wood Joints" project by Jochen Gros. It contains 50 joints that can be cut with a CNC router such as the Shapeoko, and includes pictures of the joints as well as digital files of each joint (in various formats including DXF, and IGS).

http://www.flexiblestream.org/Digital-Wood-Joints-001.php

Note - Although the download link for the 50 Digital Wood Joints archive file is broken, it can also be downloaded directly from Jochen Gros' website:

http://jochen-gros.de/A/C-Lab_files/Digital_Wood_Joints_Complete.zip

These files are open source under the Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)

50 Digital Wood Joints by Jochen Gros

An overview and discussion of traditional joinery: https://furniturefab2013.files.wordpress.com/2013/09/joints.pdf

Commercial publication on snap-fit joints: http://www2.basf.us//PLASTICSWEB/displayanyfile?id=0901a5e1801499d5

http://www.raygirling.com/wwjoints.htm http://mkmra2.blogspot.com/2014/08/cnc-cut-wood-joinery.html

Imgur: Joints from Regional Championship Denmark --- hand-cut joints w/ diagrams including: Mortis and tenon with a miter, Mortis and tenon with 2 miters, Trinity joint, Lap bridle corner joint, Sliding dovetail, Plus extension joint[3]

https://twitter.com/TheJoinery_jp [4]

Mechanical joints

Forum Discussions

Tiling

Tiling.jpg

Start with a panel the size of your supported cutting area with a pair of indexing holes at one end (a known dimension from the edge). Adjust its length until the other edge aligns against an empty area in the design. Clone the design and overlap it at that edge by twice the dimension the holes are inset. Repeat until one reaches the end. When setting up machining, do only those parts which are wholly enclosed by a given panel.

http://community.carbide3d.com/t/6-qts-of-oil-in-a-1-gal-pail-tutorial/5829

Hardware

Online source for 3D models for hardware: http://www.tracepartsonline.net/

One can also use hardware to join pieces together.

How to Build your Everything Really Really Fast by teamtestbot --- Instructable on different fasteners and their appropriate uses.[7]

http://www.quora.com/Engineering-1/What-is-something-useful-about-Engineering-you-can-teach-within-10-minutes-and-make-me-feel-astonished-and-fascinated [8]

http://www.boltscience.com/

Fasteners for stacked items

Keychains

http://community.carbide3d.com/t/weekend-project-5-carbide-keycore-system/3455

Shafts

Threaded Inserts

Various sorts of threaded inserts are available.

Some may also be paired with specialty tools for installing them:

Youtube video noting some techniques (but with some inaccurate information as well): https://youtu.be/tIhEqoKE8Dc [10]

Thread specifications

Min. number of threads in aluminum: 3[11]

Bolts

Bolts are of course a fundamental fastener type, too broad to cover here in specifics, but there are a number of accessories available for them which are worth noting:

Thumsbscrews

These can be surprisingly useful beyond their ostensible use to ease fastening by hand.

3D printed

Hinges

Wooden Box with hinged lid --- http://www.woodcraft.com/articles/426/boxes-with-pin-hinges.aspx

http://sawdustmaking.com/woodjoints/hinged.htm

https://www.reddit.com/r/woodworking/comments/5ii0u3/olivewood_box/

Notes on measuring a hinge to fit into a project: http://community.carbide3d.com/t/folding-bookshelf/5762/5

Bearings

Installing bearings on a shaft: http://community.carbide3d.com/t/proper-way-to-insert-a-bearing-into-a-shaft/4991

Joints

https://bornity.com/constant-force-joints [13]

Fasteners

Torque

Metal fasteners are an elastic system, which will only hold properly if stretched to a suitable degree by the application of the correct amount of torque.

References

http://webstore.ansi.org/fasteners/torque.aspx

http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf

https://www.boltdepot.com/fastener-information/Printable-Tools/

http://www.boltscience.com/

https://engineerdog.com/2015/01/11/10-tricks-engineers-need-to-know-about-fasteners/?wref=tp https://www.quora.com/Engineering-1/What-is-something-useful-about-Engineering-you-can-teach-within-10-minutes-and-make-me-feel-astonished-and-fascinated [14]

Magnets

http://www.kjmagnetics.com/products.asp?cat=1

Glues

A good reference site for selecting adhesives for different materials is: http://www.thistothat.com/

A useful technique for applying glue to box joints is shown in https://woodgears.ca/box_joint/more.html

Plastics

Acrylic

  • Weldon/Acrylite[15]

2 part epoxies also work.

Styles of Cutting

Drilling

One option for holes which are in a different plane than the endmill can cut is to put a notch at the edge for locating a bit for manual drilling.[16]


V-engraving

Carbide Create has direct support for this, and an excellent opensource tool is F-Engrave.

See:

Inlay

http://inlay.com/inlay/index.htm

Chamfering

Post-processing Cuts

Corner chisels can be used to clean up pockets.[19]

Another possibility is to mill a narrow groove in a material suited for bending and then form it into a shape. http://www.reddit.com/r/shapeoko/comments/32zxej/a_really_good_shapeoko_companion_tool/

Cuts in metal can be deburred: http://www.grainger.com/category/machine-deburring-tools/finishing-supplies/machining/ecatalog/N-c3b [20]

Other useful tools

10 x 10" Vacuum Forming Table

Finishing

Engraving

  • Different coloured cut areas

Polycarbonate V-engraving: put acrylic paint in the engraving (it gets all over the whole surface, but you have to force it down into the engraving), let dry, then use rubbing alcohol on a cloth to remove paint from the surface. This leaves a clean in-fill if you wipe carefully. then spray clear-coat.[25]

Vendors

Metals

For marking engravings in metal, the traditional thing is a lacquer marker: Lacquer-Stik Paintstick --- e.g., https://www.amazon.com/dp/B00Y3IOFS8

Brass

Patina solution --- http://www.sculptnouveau.com/Details.cfm?ProdID=78&category=6 [26]

Alternatives

An alternative to engraving would be to use a drag knife to cut a resist mask and then chemically etch the material.[27]

http://www.instructables.com/id/Salt-Water-Metal-Etching/

Removing Fuzz

Metals

Aluminum

https://www.reddit.com/r/CNC/comments/5dij80/how_to_best_polish_aluminium/



Aluminum Rectification.

It's basically going from one grit to the next progressively. Never jump double the grit size, keep everything clean.

The trick is after the 4k wet paper is used, to switch to Bon Ami. It's a common household cleaner that's over 6k grit. Beyond that, theirs talc at over 8k. You mix the powder with filtered water to make a thin slurry.

After that, you use a heavy paste wax (I like Johnson and Johnson) to seal the surface, before it oxidizes. At this point it'll be a mirror surface. If done right, it'll lack the wavyness of a buffed surface.


[28]

Anodizing

Lye can be used to strip the anodizing off of aluminum.

Primer

http://protective.sherwin-williams.com/detail.jsp?A=sku-26000%3Aproduct-6787 [29]

Wood Finishing

Food safe

http://www.finewoodworking.com/how-to/article/food-safe-finishes.aspx


Types of finishes

https://www.reddit.com/r/woodworking/comments/1k8c18/help_how_should_a_beginner_woodworker_finish_out/cbmfsh8/

Drying (true) oils

walnut oil, Boiled linseed oil, and Tung oil

Mostly natural oils that dry and harden in the wood.

Oil/Varnish blends

Tung oil Finish, Danish oil, Antique oil, Odies oil, tried and true oil

Oils mixed with varnish and solvents

Film building finishes

hellac, lacquer, and polyurethane

Shellac

One of the oldest finishes.

Burnishes well with kraft paper.[30]

Specific woods

Walnut

Slick walnut finish

Ebony

https://www.reddit.com/r/woodworking/comments/5db2w2/ebony_raven_pocket_knife/da3rhu3/

Stains

Coffee

https://www.sustainmycrafthabit.com/blog/2016/8/6/diy-natural-coffee-wood-stain-and-beeswax-furniture-polish

Barnwood

Darken wood with a torch and then sand.[31]