Grain Direction when machining

[martin54]

Having a background in mechanical engineering & not having done any woodworking since I was at School more than forty years ago I am a bit lacking in woodworking knowledge

I was machining a bit of Yew today, dome shape which was a slightly altered version of Michaels Vase project (thank you Michael) it's the first time I have ever machined Yew & when I started the finishing cut (3mm bn 8% stepover) I stood watching it for a few minutes & then noticed it was machining with the grain. Now I have done a few dish shapes with models in & I normally cut across the grain so stopped the machine & redid the toolpath to cut across the grain, started cutting again watched for a few mins & then left it to get on with something else. When I looked a little bit latter there were a lot of marks in the surface, first thought was that there was a problem with the machine but I couldn't see any consistence in the marking.

I reloaded the other tool path that cut with the grain & ran that watching carefully for a while & it seemed to be machining OK so left it running, it has cut perfectly on the uncut part of the back & also the front of the vase.

Haven't had a chance to check the machine so still could be a problem but why would it cut so differently on the 2 toolpaths ???

[Rcnewcomb]

Since you have the mechanical engineering background this paper may be of interest to you: Structural and Mechanical Properties of Yew Wood

Short answer: Some wood species machine better when you cut with the grain. Others machine better when you cut cross grain.

[martin54]

Thanks Randall, love a bit of light bed time reading

Ok so if some woods cut better across the grain & some cut better with the grain is there a chart or table which lists the best way each type of wood cuts or is this something that you just learn through trial & error ???

[bravesoul]

Martin,

Your pieces look really nice, so far for me it is trial and error but it would be nice if there was some sort of table that showed which wood species cuts best with one type of cut.

Joe

[martin54]

Thanks Joe, Yew is a lovely wood, made shelves & a coat rack from it for the house lol, this is the first time I have actually machined it though, cut really nicely once I had the machine going the right way. The sawmill where I buy most of my wood don't always have it but when they do it is difficult to resist the temptation to pick a bit up

Yes I would like to know if there is some sort of chart or table that would help with best cutting direction for different woods. being quite new to a lot of this it would be really useful.

[esteeme1]

Hi Martin,

Try cutting at a 45 degree raster. that may help.

[martin54]

Hi Martin,

Try cutting at a 45 degree raster. that may help.

It cut really well along the grain Jim so I know I can get good results cutting that way, nice to know it's not a problem with the machine

Will have to try some experimenting now cutting different woods at different angles, looks like I am going to have to add a section to my notebook for wood cutting direction

[ger21]

Yes I would like to know if there is some sort of chart or table that would help with best cutting direction for different woods. being quite new to a lot of this it would be really useful.

Just always cut with the grain, unless you see a problem. It works better in most cases.

[TReischl]

Lately I have been doing a lot more handcarving. I had forgotten how important it is to "cut with the grain", picking up a gouge reminded me very quickly. One thing I have noticed is that "with the grain" is not always "with the grain". Just cause the tool is moving parallel, more or less, to the grain lines does not mean it is cutting "with the grain". Sort of like making sure the grain is going down hill when planing or jointing.

What surprises me about your pic Martin is how pronounced the difference appears to be!

You sure you had the stepover set to the same value in both paths?

On another note, I was making my lovely wife a form for her pottery stuff today, just a cylinder about 5 inches in diameter on the rotary. Lunch time rolled around so I thought I would use the "pause" function in Mach 3. Hit pause, it paused. Came back, figured I would hit the Start button, so I did, message came up about a prep move. Blew right on past it and sure enough, the .5 end mill headed for China! I am going to have to read up on that function again. Turned out ok though, it was in a part of the wood that was getting cut off anyhow. Been making all sorts of half spheres on the rotary for her, all sorts of different sizes up to 12 inches diameter.

Back to cutting "with the grain". . . On most 3D type projects the tool will eventually have to go against the grain no matter what. Amazing anything comes out looking good!

[martin54]

Thanks for the advice people, I must have picked something up incorrectly at some point in time because I thought with 3d models it was better to cut across the grain . will have to delete that from my memory banks lol

Ted yes same stepover 8% I used the same toolpath I had originally but just altered the raster angle to 90 degrees.

[scottp55]

You probably caught it from me Martin:)
Almost all my small ones in Cherry/Sugar Maple/Black Walnut/Bloodwood are cut against the grain after I experimented with several bit and cutting strategy.
My stuff is so small it's almost impossible to sand without losing detail, and best results were against the grain, or offset/conventional if the model allows.
Cutting a nice little 3.5X2.5" one right now in Cherry with lots of fine detail (Beaver fur):)
scott

[martin54]

No idea where it came from Scott, now I have to work on eradicating it from my memory

Still some work to do but they aren't looking to bad now I have cut them the right way

[scottp55]

Not bad at all!!
scott