View Full Version : Cutting Techniques

05-08-2003, 12:46 AM
Fred Smith said---
"The power required to Climb mill, compared to Conventional milling is approximately 1/3. You can significantly increase your material removal by climb milling, provided your machine is backlash free and has the structural strength to stabilize the higher cutting forces and speeds"

Is the Old ShopBot PR strong enough and backlash free enough to do Climb mill cutting? Does Climb cutting cause more chattering? How does every one aproach their cuts? Cuting poll 101.

05-08-2003, 01:35 AM
David, you may also want to look at this (http://www.talkshopbot.com/forum/messages/1038/1504.html) thread.

I get the impression that very few ShopBotters actually care about the difference - because they wouldn't know how to switch the direction. Making provocative statements 101.

05-08-2003, 07:05 AM
There are many "what ifs" invovled in the choice between climb cutting and conventional cutting. The shopbot will handle climb cutting up to a point. If you wanted to climb cut white oak with a 1/2" bit at 3/4" per pass with a 2" per second feed then probably, no. But then it wouldn't convetional cut at that either. I don't think it takes 1/3 the power, you're still removing the same amount of material with the same cutter which takes the same work. I cut both styles based on experience with different materials, cutters etc. An example is 3/4" Elliotis plwood of which we often cut several units a week of. If edge finish isn't critical an up spiral bit doing a climb cut is an ok choice. If edge finish is important then I get the best results with a compression spiral with a conventional cut. I can cut both at the same rate it's just the spiral bit is cheaper than the compression spiral. Plastics often, but not always, cut better with a climb cut as is also true of solid lumber. Experiment and as you gain experience you'll find what works best for you. Just remember that you need a stiff bit to climb cut, I rarely use 1/4" cutters but never for climb cutting as there is just to much deflection.

05-08-2003, 08:03 AM
Fred Smith's comments are probably based on the power it takes to move the bit in the wood. If a tool has 100% feed, 1/2 the cut is "climb" and the rest is "conventional".

Wood is not near as mean or demanding as metal. If one is working on an old "loose" mill with backlash and/or "flex", partial bit cuts combined with "climb" milling sometimes results in the bit pulling itself into the work. The bit starts taking more aggressive bites as the slack is taken out of the drive screws and ways. Depending on the material, bit, clamping, condition of tool and operator "savvy" interesting things start to happen. Material and pieces can become airborne projectiles and this tends to cause things to go "Out of Spec". Blood is not easy to clean from machine tools and causes rust.

05-08-2003, 08:27 AM
My comments are concerning the spindle power requirements. Climb cutting requires less spindle horsepower due to the cutting forces involved with material removal by shearing (climb cutting focus) vs rubbing (conventional cutting focus).

Less heat with climb cutting for the same reason.

Fred Smith - IMService

05-08-2003, 09:04 AM
The actual power consumption (amps drawn by the router) is definitely not 3 times higher for one style of cutting over the other. Those with ampmeters among us can easily confirm this. During a practical test today, I could not measure any significant difference, but Ron will probably laugh at my African ampmeter. (hold two wires on tongue and see how far your toes curl up. . . . . . )

05-08-2003, 11:27 AM
Thanks for the clarification Fred.

It is obvious you don't have a 480 Volt router Gerald.

05-08-2003, 11:41 AM
The only time I even think of climb or conventional is if I am routing the edge of a board, and then also if the grain pattern is of a type that will tear Like hickory etc. if you are routing in the middle of the board as Ron B. was puting it you are in essence routing 1/2 climb 1/2 conventional. David in Wyoming

05-08-2003, 04:15 PM
PapaDave, Most of the edges of my toys need nice edges. I did a little experiment in the shop today.

I took my 1/2 baltic birch board and I rounded over the edges with a double roundover with a bearing in the middle. I pushed the board from right to left against cutter and then I tried it going with the cutter. Going with the cutter made it much easier to cut, but it didn't leave as nice a cut.

Bye the way the round over was only 1/8 diameter of an inch so it dosn't have much "Kickback ability".

I'm guessing (Since I'm not educated in these matters) that the "decreased power thing" is because the cutter literally drags you along when doing a climb cut. When you are doing the conventional cut your machine has to push against the direction of spindle circular cutting motion.

05-08-2003, 04:59 PM
David I just went to your web site, I'm glad to see the Bot being used in this way. David in Wyoming God Bless

05-08-2003, 11:32 PM
David, if the cutter is "dragging you along", then the cutter does more work and therefore the cutter needs more power. Confusing?

05-09-2003, 12:20 PM
The way I see it... it takes less power to push [from the shopbot] the cutter along when climb milling. I don't think the cutter is doing more work, but the energy is put more into draging than cutting and thats why the cut is not as good. But when going against the rotation of the cutter[conventional] you need more force to overcome the rotation of the cutter. And the router now has more friction [shopbot pushing against its rotation] to overcome and requires more power to do the same cut, however that cut is much nicer.

I guess this only applies when cutting on an edge as apossed to hogging through the wood with the whole cutter.

05-09-2003, 12:57 PM
David I am doing a research that may help you alot with your toys, I have a friend in Colorado that makes custom doors and molding. He uses a machine that holds a profile sanding spindel it is power fed and all, now I know these machines cost two arms and 14 legs but if I can find a profile spindel that has the double roundover you do on the toys you could build a platform for the spindle and hand feed it. It would be attached to a say 1750 rpm motor via pullies etc. David in Wyoming

05-09-2003, 02:32 PM
PapaDave, I would love to find out more about that. I have for a long time wanted inprove my sanding ability. It takes a long time and makes the toys too expensive for most parents. Grand parents buy the most toys. Right now I bearly have any arms or legs. We havn't sold much so please tell all your friends and family about us and our mission. We need all the help we can get. I'm constantly trying to improve on my cutting ability and thus the reason for restarting this topic.

Here is a twist, what if you made your shopbot osilate up and down through a cut would that could that make a smoother cut due to the randomness? Like an osilating spindle sander?

05-09-2003, 06:09 PM
Larick makes a profile sanding head.


05-09-2003, 07:01 PM
David, Sheldon beat me to it. This is the same company my friend uses if you look at the sanding wheels they will custom make them to your specs and they use a 1" arbor, you could get a cheap shaper and use this for all your edges. Also somewhere in all my software I have a program for doing puzzles it will take a bitmap or a jpeg and convert it to a puzzle cut out and then you only need to save as DXF. It will give as many or as few pieces as you need. I will look for it but alas I am in the middle of tearing down my shop to move out.will get it to you asap e-mail me your address dands50@hotmail.com (mailto:dands50@hotmail.com) David in Wyoming

05-31-2003, 08:57 AM
I'm spending far to much money on tooling to cut 3/4'' melamine with a 1/2'' up cut spiral bit. I know the rpm of the router and the travel cut speed have much to do with the quality of the finish. As you know melamine chips very easily.
All the cuts are with in the material edges so no climb cutting is involved.

05-31-2003, 10:25 AM
I guess one obvious question would be; why an upcut spiral bit? Have you tried "straight"bits? it would seem that ANY bit with a pre-determined up/down orientaion would have to tear out either the top or bottom of your melamine. . Even a compression bit might be a better option since in theory it cuts towards the center of your piece from both the top and bottom..

05-31-2003, 06:34 PM
We cut melamine with a single or double flute 3/8" dia. Onsrud compression spiral. Typical feed speed in 3/4" is around 2" per sec at 12,000 rpm (we have a columbo spindle). The results are usually excellent and the 3/8" bit is a good compromise between stiffness and cost. Onsrud makes a compression spiral with a very short upcut section that helps keep parts on the vacuum table when cutting alot of smaller nested parts and we use them extensively. Bit life is usually one and a half to two 8 hr shifts. They can be resharpened about two or three times before it's time to pitch 'em. After resharpening they do not seem to last quite as long but for the price it works out well.


06-01-2003, 02:34 AM
Eric, what is your price on a new bit and cost of resharpening on those Onsrud bits?

My impression is that a lot of the up-cut spiral bits being used out there are not solid carbide and are not designed for cutting soft material like wood or plastic. The metalworkers often use HSS (high speed steel) milling cutters (or "slot drills"} that look great, but don't give anywhere near the life of solid carbide Onsrud or Belin bits. The metalwork bits have a blunter rake angle and less space in the core for the chips to move out of the cut. Metalwork bits are not designed for anywhere near to the feed speeds used on soft materials (1" - 2" per second).

06-01-2003, 07:55 AM
A 3/8" single flute short up cut compression spiral (whew!) in small quantities run about $65 us to purchase and $16 to resharpen. We can get additional discounts if we buy a bunch at once, not to mention saving a bit on shipping. While metalworking bits are cheaper you are very right in that the cutter geometry is very different. You can use them but they did not give us the same level of quality finish at the feeds we run and feed speed is very impotant to us when running thousands of parts! on a contracted price!

CNC Routing Services
06-02-2003, 01:06 AM
I also am working in baltic birch, doing climb milling and roundover. A suggestion for sanding - get a pneumatic drum sander. This is basically a rubber bladder you put a sanding sleeve on and inflate. Inflate it softly, and it will conform to your profile - sand it quickly and cleanly without hogging material off or altering your roundover. Personally got sick of trying to wiggle the boards just right to knock off the fuzz without ruining my 3/8" roundover. For bits, Magnate.net has an excellent selection, their prices are superb, and their bits are holding up quite nicely for me. Compression spiral was $35. Run 1000+ parts with it and it looks the same as the day I got it. Anyway, sorry to ramble, and hope this helps.


06-02-2003, 01:47 AM
I think that ALL compression bits are designed for wood/plastics - I have never seen them in the metalwork industry before.

Here (http://www.magnate.net/products/rout_bit/spiral.htm) are the Magnate (http://www.magnate.net/main.htm) spiral bits. We use the O-flute type (not from Magnate). The photographs of the "regular" spirals shown on this page (http://www.magnate.net/products/rout_bit/spirals/regular.htm) are interesting; The UP cutter clearly has a cone-shaped core, so there is less space for chip-clearance further away from the tip. The DOWN cutter in the photo has more space in the core away from the tip. Could it be that the up cutter is a standard metalwork bit?

06-02-2003, 06:57 AM
One thing I've noticed when running plywood (including birch) is that I'm getting cleaner cuts conventional cutting rather than climb cutting. While this runs against the standard "rule of thumb" I can't argue with the results. We don't have to sand anything except Luan and Virola and then only when the bit begins to loose it's edge. I have to admit that while I havn't tried every manufacturers bits out there I've yet to get better results than the ones I'm getting. The extra cost really doesn't matter as it's spread out over such large parts runs. After 20 years in the wood game I'm getting like an old dog, set in my ways.....

06-02-2003, 10:58 AM
I cut a Noah's ark out the other day and on one of the parts was a bunch of waxy material. What could this be? Except the hair on top and bottom this particular board also came out almost waxed smooth.

Neil, thanks for the sanding drum tip. I have been agonizing over the price of a profile spindle sander and these pnematic drum sanders are much better priced and a lot quicker to change the abrasive. Looks like I could mount a drill and sand on the shopbot
I like that idea!

Has anyone had a bad experience with these drum sanders?

Does anyone have a favorite pneumatic drum sander?

06-02-2003, 08:17 PM

I considered that, but based on volume, I went with a dedicated floor model. Grizzly has a 1 horse with dust collection for $450 delivered. 4" dust port on back end, and a 4" X 9" drum. Sleeves are $3.95 each. They have a bench model for $160, but this lacks dust collection. Woodtek also has one or more models, but no dust collection on these either.

Best of Luck,


06-02-2003, 08:56 PM

I recently bought an inflatable drum sander made in Sweden and it has worked great. Really reduces finish time on inside (and outside) contours. Page 133 Woodworkers supply fall catalog lower right hand corner. Along with the inflatable bulbs, you need to purchase a pump and a flexible shaft with a chuck in one end. Run it off a dedicated moter or off a drill press or just a drill.

This thing reduced finish sanding on what we do by about 90% and does a better job.

06-05-2003, 03:42 PM
We've been making a lot of birch ply children's furnishings, and have been rounding over all the edges with a hand held router. We'd like to make this happen (at least half of it) on the 'bot. After visiting a couple of big shows, witnessing huge cnc centers that do doors and door edges, we'd like to create "pods" that would allow us to run a bullnose profile cutter. I'm wondering what folks have done to automate rounding edges on top AND bottom edge in one pass - onsrud has a straight / roundover cutter in their new product line for a top side radius.

Anybody using these techniques? Any suggetions on where to look elsewhere on the forum?

Also, anybody cutting vinyl or linoleum floor tile? Curious.....


Matt Barinholtz
Covenant House Washington, D.C.