Bit for 1.5” length of cut in 2x8

[johnsontoddr]

I’m looking for suggestions on what bit I can use to cut a decorative end pattern on a 2x8 using my Desktop Max. I have the starter bit set, but it doesn’t look like I can cut that deep with any of those bits. As I move to longer bits I’m not sure what the max bit length of Max is. The specs seem to indicate a maximum cut depth of 3.5”.

[Tim Lucas]

try www.vortextool.com not cheep but good and sharp

Tim

[johnsontoddr]

try www.vortextool.com not cheep but good and sharp

Tim

The problem is that I'm not sure what length and width bit I should use. I assume a .5 inch diameter bit would be better to help with deflection, but I'm not sure how long an overall bit I can use in the Desktop Max with the spindle.

[Martin Reid]

Dear Johnsontoddr

The maximum length of bit and the maximum depth of cut can be calculated as shown on the attached image.

Cutter.jpg

The width of the bit will be a proportion of the length calculated by the manufacturer. If you think deflection will be an issue then slow the feed rate and reduce the depth of cut. You can hear a deflecting cutter 'singing' and if you don't do anything it will only break and take the collet with it. Some people don't change the collet after a breakage but that is a false economy.

Anyway best of luck
Sincerely and in good faith
Martin

PS further info on worn collets for those interested
http://www.talkshopbot.com/forum/sho...322#post198322

[Tim Lucas]

The problem is that I'm not sure what length and width bit I should use. I assume a .5 inch diameter bit would be better to help with deflection, but I'm not sure how long an overall bit I can use in the Desktop Max with the spindle.

I have a need to cut thick cedar for counter tops and such up to about 2 1/2" so i purchased this from Vortex Product #: 1265
DESCRIPTION: SC DE Upcut Finisher
CED: 1/2
CEL: 2 1/8
SHK DIA: 1/2
OAL: 4

my z can retract high enough to get the bit (about 3 1/4" sticking out of the router) above the material and not hit any dust collection and such, so i can use it.
look at your machine place a chunk of 2x8 on your table raise your z almost all the way up and see how much room you have then go from there.

The 1/2" bit is twice as strong as the 1/4" and when working with longer bits I would suggest using the 1/2" - they do have 3/8" bits but i dont have a collet for them.

hope this helps
Tim

[johnsontoddr]

Thanks for the suggestions. I raised the spindle up to near max Z with a 2.5 inch long compression bit installed (the longest I have). It looks like there is plenty of room for the 4" long Onsrud 52-367 to clear a 2x8, so I ordered that to try. Its cutting length is 2.12 inches, so plenty of length for a 2x8. To minimize deflection I will use multiple .5 inch depth cuts and start with Onsrud's recommended chipload for the bit in softwood.

[tomhartnett]

When you end up making the cuts/files, keep an eye out for your safe-z heights and pull-ups. With 2.12" CL and a 2" board (plus 0.5" spoil/base) you are at 4.5" or so taken up of your 5.5" Z movement. So you may have less than an inch of pull-up/space to work with above your material before topping out the Z.
The place to check in SB3 is under Values->Cutter Values (Safe Z pull-up - defaulted to 1") and if you are using VCarve/Aspire you'll find a Home/Start position -

VCarve - HomeStart position.JPG

that includes a Z location (which will be where the tool goes at the start and end of the cut file). Make sure these values are within your working Z space where the Z won't top out during the operation.

-Tom H.

[johnsontoddr]

Very good points. I use Fusion 360, which allows me to set a clearance and retract height, but I'll also need to be sure that the Home point set in the Shopbot app can handle the longer bit. A 2x8 is only 1.75 inches thick so I think if I'm careful with all this it should work.

[scottp55]

Tom made great points(and beat me to it)
Does your machine have an upper Z limit switch that prevents you from "Topping Out"...or do you hard stop when raising bit with keypad?
Topping out can have some rather dramatic movements if your not aware of it!
When working with my Desktop, VC Safe-Z pullup has been critical.
Just thought I'd toss a pic in....also maybe start directly over the workpiece the first time with the keypad in case you forgot something.
Jogging into the side of the workpiece at depth can make you spit coffee on your keyboard!
scott

VC is also nice when prototyping a thinner workpiece with it set at 2"....then you can run a few lines to make sure it's cutting right...hip Spacebar for a pause, and get your dustfoot on(spacebar pause kicks it out of the Vectric, and into the SB3 parameters)

[johnsontoddr]

I don't have a z proxy switch, though I do have the cut out bracket that could easily take one. I'll be sure to carefully set the safe-Z pullup to end above the material. I will try an air cut without a bit or material after I think I've got the settings dialed in.