Bit/Wood Recommendations

[rajanm (Rajan Mann)]

Hi everyone, I am trying to cut out a wooden sign and I find that the letters always break–I feel like it’s maybe the wood I am using or maybe the wrong bit? Any recommendations for best wood type & bit size for a wooden sign? Please see attached for picture of file & project. I am currently using 1/2 Birch plywood and Nomad bit #201

[WillAdams (William Adams (Carbide 3D))]

First, what sort of plywood are you using?

If you can source it at a reasonable cost, and aren’t already using it, try Baltic Birch, or some similar plywood guaranteed to be void free (Apple Ply is one brandname which some folks have had good experience with)

Second, are you cutting slots just as narrow as the tool?

Where possible avoid slotting and add geometry and cut as a pocket

Making vacuum hose adapters

While cutting up vacuum extension wands for this is expedient, it’s a bit problematic given that Shop Vac recently filed for bankruptcy, was bought at the last minute, and production hasn’t caught up. I need a receptacle for the Sweepy 2.0 dust fitting — one option would be to purchase one from Woodcraft, but Carbide 3D sells blocks of HDPE: which looks to be just barely big enough for things to fit. Measuring the hose fitting I get a diameter of ~63.5mm — offsetting that twice we arrive at…

and/or

Adding geometry to cut as a pocket with a finishing pass

One technique which is often suggested to avoid slotting is to add geometry around a part which one wishes to cut out and cut as a pocket down to tab depth — here’s one technique for that. In this case, the project is a bevel gauge which will be cut out of 0.0625" (~1.5mm) thick aluminum: [bevelgauge] Due to the narrowness of the angles, an 0.03125" endmill has to be used, so after importing and scaling the file (we will be cutting out one which is 3") we select the perimeter and offset it tw…

and consider leaving a roughing clearance and taking a finishing pass.

Best Bit for full cut through

One which has a cutting flute length equal to or greater than the thickness of the stock — pretty much any tool should work. Big thing is the toolpaths — if cutting out, rather than just cutting a slot: [image] Offset to the outside by endmill diameter plus 10% or so: [image] [image] [image] Then cut as a pocket: [image] down to tab height or the penultimate pass: [image] then move the contour down to below the pocket and start cutting at the bottom of the pocket: [image] and…

[Zman (MICHAEL ZEMANEK)]

Did you use tabs on your design to hold the part steady?

Or

Depth of cut might have been aggressive causing pressure on the part in those areas

[gdon_2003 (Guy Donham)]

Plywood is layers of wood that are laid down at 90 degree angles to each other. They are glued together and sometimes the glue is not evenly spread. Plus a lot of plywood has voids below the surface in the layers. Maybe using poplar or another hardwood would work better.

Unfortunately fine detail even on hardwood might break off from the stress of the milling operation. I use very little plywood in carving projects because of the above problems with plywood.

Will Adams always recommends that if possible to not do a contour cut the width of the cutter. When possible make the contour around the object wider so the bit makes two passes at each layer. When cutting the width of your bit there is a lot of stress put on the wood and it can snap off. When the bit makes curves it can be pulled slightly off course by the cutting action. Plywood is even more susceptible to breaking due to the cross lamination.