Need help with clean bottom pocket cuts

[mmak2916]

Attached is an image of the pocket toolpath I'm trying to achieve. The material I'm cutting through is 0.750" and the pocket depth is 0.350". The rectangle is around 2.25" x 2", the protruding circle is 1.250" diameter.

I'm using a 1/4" downcut spiral bit (Onsrud 57-910), ramp cut, Clear Pocket: Offset / Climb. However, there's noticeable tool marks on the bottom of the pocket. Is this not the bit to use or can this be fixed with the correct toolpathing?

Is a compression bit not a good choice for pocket cuts?

Thanks!

24417

[Brady Watson]

A compression, upcut or straight would be better than the downcut. The chips get forced under the cutter and give a poor bottom finish. Onsrud does make a downcut designed for cleaner bottom cuts, but I don't know the number off the top.

-B

[scottp55]

M,
How deep is your last pass?
Birch again?
Is circle far enough(how far is it?) from right sidewall to use an pocket allowance? (rough pass shown)
Have had good luck with Centurion FEM Downcut on some woods hogging out waste in first pass and leaving a .015" skin on both walls and pocket bottom, and then do a full depth pass at lower stepover and taking the "Skin" off.
Hogging against the grain, and finishing with the grain work best in most cases for me, BUT sometimes/some woods offset path is cleaner as you can control climb/conventional.
Play with it:)
scott

[srwtlc]

I agree with Scott, a FEM downcut and leave a small allowance 0.015-0.020 on the bottom or both bottom and sides and run a full depth final pass. Raster with grain is usually the best. Centurion also makes a FEM compression bit that works well too. The FEM bits don't leave the 'swirl' pattern that regular up/down/compression bits do on a pocket bottom.

[mmak2916]

Hi Scott,

I'm working with walnut wood this time. I can't tell the depth of the last pass because I'm doing a spiral ramp, but my bit is set at 0.250" pass depth.

I will try your method regarding the "Hogging against the grain, and finishing with the grain" with my compression bit and see how that goes first. If it doesn't work out too well, I'll get an FEM bit, is this one you'd suggest?
https://www.centuriontools.com/router-bits-toolcase/solid-carbide-wood-router-bits.html?sku=14DS21.253FEM

Thanks!

[scottp55]

M,
Yes, That's the one, I also got the the 1/2" and same excellent results for larger pockets.
Spiral Ramp Pocket?
Black Walnut seems to be picky for RPM (for me at least), so listen to the bit and watch chips. Great wood though.
May play with scraps as those feeds/speeds in pic look like old defaults on this laptop. Will post control computers "Tweaked" walnut ones.
I'll try to post some pics later.
Scott W.,
Pretty sure it was you that turned me on to the Centurion FEM's when I was doing Biz card holders pockets that were a size that were a PITA to sand.
Thanks!:)
scott

[srwtlc]

If I don't need the extra cutting edge length, I always opt for the shorter 1" CEL (used to be able to get 0.875" CEL) because the longer the bit, the more susceptible it is to 'singing' or vibration, which translated to the cut. If I can, I'll always use a 0.375" bit before a 0.25" bit, as it leaves me a much better finished edge.

Walnut, for the most part, cuts nice and clean unless you get into some sapwood areas. I once had a batch of walnut that I swear was a cross between walnut and it's cousin butternut as it was so stringy that I couldn't get a good cut on any machine no way no how.

[scottp55]

M.
Didn't have a scrap of B. Walnut big enough to do many tests, but did have some Sugar Maple I could cut down flat and still have enough thickness to do some .03"deep pockets(and still get my buttons after surfacing again.
Board was surfacing down with the Centurion.25"D FEMDowncut while I organized shop in .02"deep passes ---(so outside pockets is .02"passes and hit with a quick 220G)..
Only had enough material to do .03" deep without wasting wood.
I get best finish with a last pass of .015-.2" and just testing for myself what the differences were in cutting strategy, as it's been a year since I did any testing, and thought I might have been stuck in a rut while better options were out there.
Set up 7 of yours, and then tried offset(climb/conventional),rasters(both with And against grain) and a couple of speeds(but default pocket speed of 1.5,.5,9K was still the best).
Only simulating a slightly thicker than normal last pass for me, so NO offsets.
WAS going to run another in .02" pass in Walnut, but ran out of time.
Like #'s 4(offset) and 7(raster/with grain).
4 is better if lightly touched with 220G, and 7 if left unsanded. BUT notice a couple of tears in pocket bottom(small but there) which may be what Brady was talking about pushing waste into the cut and chip pulling a fiber up?
WAS going to try an Upcut and Straight, but again ran out of time.
E-mail me if you want .crv and other 5 pics anyone.
Good luck M.
scott

[scottp55]

Oh, Thanks Scott.
Never really thought about CEL changing it as much as the overall length/Diameter of shank.
In my case, needed it for cutout of 1.15" stock, so wouldn't have changed my order.
DO need to get on the stick about getting some 3" brushes for my dustfoot, as 3" cutters have to0 many "escapee" chips with the stock 2" Desktop brushes.
Wish they made it in a 2.5" :)
scott

[tommy tomlinson]

I have had good results with a .25" ballnose with a 20 percent step over.

[scottp55]

Darn,
"I get best finish with a last pass of .015-.2" "
Should be .015-.02"

Oh, M,
Only reason I use against grain for roughing passes, is quite often you get long splinters that can Jam in Desktops 2.5" DC and almost always stick on grounding wire inside hose which is difficult/time consuming to remove.

[Brady Watson]

I don't use many 'router bits' and don't readily recognize the term 'FEM', so I had to look it up. FEM = Flat End Mill, which is a router bit term, not an industry standard metalworking term.

Most woodworking spiral tools have a swallow tail tip on them that don't do such a hot job for pocketing. Solid carbide center cutting end mills have a flat bottom, but their shear in an upward direction. There are such things as left-hand end mills, which also are center cutting, but down cutting.

-B

[scottp55]

Just trying to use Centurions terminology to make it easier for people to search/find.
Thought I remembered seeing some beautiful pocket finishes using Onsrud (Chipbreaker/Finisher? Mr.Beckwith? Paul Nast?) in hardwoods, but can't seem to locate it:(
LH CC EM's seemed to confuse people a few threads back this year, and thought the "angle" was very difficult to nail down and the very slight "Domes" in tight spaces were a bear to sand flush accurately?
What's the "Flattest" Left Hand Center Cutting End Mill you've run across Brady?
Money is tight until Etsy is going later this week.....Always feel guilty when I spend Dad's money on a bit, and THEN it doesn't work as well as I expected:(
Thanks Brady
Still working to contact my friend with the Chinese Amber "Dragon" for you to Scan, But she's dropped landline and changed cell#?
Thank you for your offer, and VERY interested in how well and detailed I can recreate such an intricate/Unique item from such an accurate 3D scan:)
Figured I'd offer her a 3-4X scale "Dragon" in Ebony or Snakewood(Got a beautiful handmade Valentine's card from her and May resort to snail mail)
Rambling,
scott

[Brady Watson]

A standard center cutting (upcut) end mill will give a clean bottom. However, it may cause some tearout on the top edge. Something like a garden variety Bosch 2FL downcut spiral router bit will give a clean top edge, but fuzzy bottom edge because it has a swallow tail on the end of it. So I can certainly see the value of an FEM here. If you don't mind a bit change, you can use any el cheapo downcut for the top edge (say .125" deep), then change to and upcut spiral end mill - which should be center cutting, to get a nice clean bottom. This doesn't make any sense if the FEM can get it in one hit though.

No problem on the scanning stuff. Let me know when you're ready.

-B