Help request for bit selection

[mzettl]

I need some help selecting the best bit to cut Brazilian Cherry. The material that I am cutting is 1.75 in. thick. This is a very hard and dense wood, slightly denser than hard maple in fact. I am cutting 16" x 22" pieces out of blanks that are 17" x 23." I have used both a 1/2 in. downcut spiral and a 1/2" straight bit, making a roughing cut in 4 passes at an offset of 1/32" from the finish outline. This was followed by a finishing cut in two passes with the same bit.

I have utilized the information on chiploads in the Onsrud catalogue to determine feed rate and RPM. I am having problems with chatter marks in both the roughing cut and the finish cut. I have experimented with feed rates ranging from 80-120 inches per minute and RPMs ranging from 9000-12000. Thus far, the best finish seems to come with a 1/2 in. spiral at 12,000 RPM and a 120 in/min feed rate, but I'm still getting chatter marks with these setting.

I am using a ShopBot Alpha with a HSD 4.3 HP spindle.

Ideally, I would like to do the roughing and finishing with one bit, but this may not be realistic. My goal is a finish cut that requires very little sanding to achieve a very smooth finish. I would appreciate any recommendations regarding the optimal bit or bits to achieve this end. Additionally, I would welcome recommendations regarding feed rates, RPM, stepdown, stepover, etc.

I've reviewed various threads on the ShopBot Forums that might pertain to this situation, but haven't found anything with the information that I'm looking for.

Finally, I would like to add that I have e-mailed Onsrud twice within the past two weeks with a detailed description of my problem, setup, trials, etc., and asked for their advice. I have yet to receive a reply. I realize that I'm not a big customer, but it's disturbing that they won't even give me a cursory response.

Thanks in advance for any help or suggestions.


Matt

[richards]

Matt,
Are you only getting 'chatter' marks with the Brazilian Cherry? How about MDF? Chatter is a problem that has plagued many of us who own Alphas. I had to build and install a 3:1 gearbox on each of the X/Y motors before I got chatter-free cuts. Before adding the gear boxes, I tried as many different cutters as I could buy locally, including several from Onsrud. As it turned out, the problem was not the cutters, feed speed or spindle speed, it was inherent in the machine. The gear boxes solved the problem.

[mzettl]

Mike,

Thanks for your input. I've actually read your posts regarding this problem with some interest. I've only had my machine for 3 months, so I'll admit my experience is limited. Although I have noticed some chatter with other materials, it has not been this noticeable. Also, I have used a 1" Onsrud tray bit on this same material, making a 3/4" deep roughing cut, and a 1/32" finishing pass with virtually no chatter marks at all. That is what makes me think that it is something that is not inherent in the machine, at least not totally so.

Nonetheless, your thoughts are worth consideration, and I think some additional experimentation is in order. I certainly am not anxious to go out and buy a bunch of new bits, and then find that I still have the same problem.

Matt

[terryd]

Matt,
Did you try the first cut as a "climb" cut then reverse the direction for the final cut as a "conventional". Or vice versa. I have an Alpha and cut hard maple on a regular basis. I run 1/2" upcut spirals at 1/2" depth per pass ofset outwards 1/32". Cut speed is 2.5 inch/sec @ 16000 rpm. with a Porter Cable. Using the same bit I cut in the opposite direction full depth @ 20000 rpm inset 1/32". I adjust the feed speed until I get clean chatter free cuts with no burning. I did the chipload calculations and then I learned from experimenting.I have conluded that each load of lumber is different therefore the cutting parameters must change also. Generally the final pass is where "chatter" matters so if I have to essentially sand the perimeter with the bit then thats what I do. My 2 cents worth

[terryd]

Matt,
I almost forgot, if you are cutting 1.75" material then you will have to have a cutter with cutting edge length of 2". No matter what you try you will never achieve a "perfect finish" if your entire edge is not in contact with the cutting edge at the same time. If you do use a cutter that is too short the top shank portion acts as a coller and will duplicate all the surface imperfections to the next layer.

[mzettl]

Terry,

Initially, I used a climb cut on both passes. Then I tried a conventional on the first pass - big mistake, as I had some bad tearout that was too deep for the finish pass to clean up. At that point I abandoned conventional cuts.

Maybe I need to increase my RPM much higher. I certainly agree that the chatter on the initial cuts is of no concern, it's the finish cut that's important. I think I'll try that as well as doing a convetional on the final pass.

Thanks for your input.

Matt

[paco]

Terry, mind telling me which bit you use with those settings?

I happen to have to carve large piece out of Birch block and so far I cannot achieve as aggressive cut as you do (1/2"CED, 1/2"stepdown, @2.5"/sec., @16000 RPM).
I actually don't care for the finish since I use the 1/2" CED for roughing. I'm considering the Onsrud 60-905 but it is not a cheap tool... I would be more in the budget of the 52-936... any feed back about those?

[terryd]

Paco,
I generally use Freud 75-108 upcut spiral solid carbide 1.25" CEL 3" overall 1/2" shank and cutting diameter. For some reason this bit works better than most, seems to have a steeper than normal spiral. BTW I cut birch also and find that it is a "stringier" wood and usually require that I change my stepdown to 3/8" per pass. The bits are the same price everywhere, direct from FREUD or a reseller. Around $40 canadian @ Home Despot. I also use DIMAR bits but for solid hardwoods I keep coming back to Freud upcut spirals. Their other stuff is pretty much standard grade. I prefer that the bit break than flex and I suspect that the Freud carbide is more brittle than most.

[simon]

Please go to this (http://www.rainforestrelief.org/News_and_Events/News_About_the_World_s_Rainforests/New_York_Times_on_Illegal_Logging.html) site

[wcsg]

YEEEEHAAAAWWWW where's my chain saw?!?!?

[Ryan Patterson]

I cut some brazilian cherry today for stair treads 1 1/2" thick. I used a 3/8" sprial up at 18,000 rmp with feed at 9"/sec. I cut in four passes with no finishing pass. The edge I got was clean.

[jseiler]

simon,

how about this?

http://tropicalhardwoods.com

[mzettl]

Ryan,

Can you tell me exactly whose 3/8" bit you were using, and what # it is? What type of spindle/router do you have, and are you using a PRT Alpha? A 9in/sec feed rate is beyond anything I would have imagined.

Matt

[Ryan Patterson]

Matt,
I have an Alpha with 3HP Colombo. The tool I used is from MasterCut Tool #801-2823. I am set up as a disributor for MasterCut if you can not find someone in your area I would be happy to send one to you. I am not at the shop but I think they are priced at $27.00.