Stepover?

[Kym]

Hi,
New to this machining.
I have the model "Last Supper Dish" and am trying to work out the best stepover size .
The carve size is 400mm x 165mm. The tool is 3mm Diam Ball Nose End Mill.
What would the recommended stepover size be, to create a detailed finish.eg - 0.2mm?
Obviously the smaller the stepover the longer the machine time,but detail is what it is all about.
Cheers........Kym

[JamesB]

10% of the tool diamter or less is the rule of thumb. So your 0.2mm should definitely be good enough if the tool is sound.
Regards,
James

[Thkoutsidthebox]

FWIW...

Reducing your stepover is going to improve the 'quality' of your cut, and reduce the manual sanding afterwards. It is not going to improve the 'detail'.

To improve the detail, you have to use a smaller diameter bit.

[Kym]

Thank you for the info on stepover.
Cheers......Kym

[gravirozo]

hi..

i just run the second of this pattern, i have the "A" withouth background and dish... i have been set for 200x680 mm the size, and the 1/16 a little over like 1.5 mm still don't pulll all detail up... i choosed 0.22 the stepover....
the surface is smooth... but some detail still require smaller bit... for your size, you given, might need around 1/32... i mean, for all detail...

also can be limiter your computer memory... this picture generated me a 9 meg file... after i did set the output just for two digit (after the floating point, precisity) still the file 8 meg.... i use 2gig mem... and this file test my computer just be patient... my machine run night,,,, while i sleep

[js11110]

hi..

i just run the second of this pattern, i have the "A" withouth background and dish... i have been set for 200x680 mm the size, and the 1/16 a little over like 1.5 mm still don't pulll all detail up... i choosed 0.22 the stepover....
the surface is smooth... but some detail still require smaller bit... for your size, you given, might need around 1/32... i mean, for all detail...

also can be limiter your computer memory... this picture generated me a 9 meg file... after i did set the output just for two digit (after the floating point, precisity) still the file 8 meg.... i use 2gig mem... and this file test my computer just be patient... my machine run night,,,, while i sleep

For a 1/16 cutter (1.5mm) I would finish with a .005(.125mm) stepover.

Jason

[gravirozo]

hi

i'm going to give it a try... on a smaller pattern... the last supper for me already over 10 hour...
i agree totally, we have to finish on the router, because the sanding is not an option, #1 the time, #2 the details, and the quality...
might be a large size where already used 1/4 for finish...
and as you make less and less the stepover the file grow drastically... in the shed, i have 2 computer with 128 meg ram, they already can't compute the horsehead... the rough yes, but the finishpass already too much for them..
the controller program is not limited... that just open the file and start to read...

here's apicture, i work on ... these plates already took days... i just on the finishing of the bottom...

the four smaller, made out of basswood, and the supper made out of hard maple...

for the basswood, due it's soft i used hss, and for the maple i used carbide...

[Kym]

Hi Gravirozo,

What amount of RAM would be recommended to handle these large files?

Do you run a small router when machining with small diameter bits and for these large files that take hours to complete?

I suspect when machining timber it will always be necessary to have some finishing sanding.

Cheers......Kym

[gravirozo]

hi

Kym.... the ram necessary, hard to find out the real amount of... what i experienced, when i bought the last supper, and tried to load, i got trough on the rough, but the finish pass calculation stopped all the time around 60-70 percent... and i got message, out of memory... after i bought 1 gig (now i have 2 gig) my computer got a litttle faster and could finish the computing...
the machining time... there's a virtual time, you get when you compute the toolpath in the machinist... and your machine perform....
a servosystem basically faster, but any way, each node slow down the machining... even a staraight line, if you place several node on a line that be slover like without nodes...
in a picture, in this case the last supper, has 5 line per mm multiplied with 680, 3400, and this number multiplied vith several hundred, as the z level changing within one pass... it's real when you set the finish pass for 0.2mm
so, even a fast servosystem, which one try to keep the speed, but when it get a "sharp" corner, it must to slow down, just like a car...
so really accelerate the processing, only way set higher the pass. but on that way you loose detail... still with this size i used, and this is not the dished outline...
still i feel i should use smaller bit to finish and passes should be around 0.12-0.15 as some one remarked here...

so summarized, if you use win xp, you need the 2 gig memory...
about sanding,,,, the optimal 6-8 percent of moisture in the wood (humidity) rare to becomes... with that, and sharp bits, right rpm, you can be close to no sanding...
but when a wood is not dried totally it's fibers are flexible more, an they can not be cut so well.... the ideal cut for wood like when you sharp a pen... that s rare...
when u use bits, they push down the fibers... and the stain and paint raise these... that's why you feel the ""hairy"" after first coat of paint...
i think randall newcomb said right on a topic "the bigger is better" as mean, the customer impressed more with a larger project, and due to above details, can happen you cut a larger project in same time...