A few elementary questions

My Shapeoko XL is on its way and, hopefully, should be here on Wednesday. I’m looking forward to getting it together and to actually start doing something with it rather than just reading what others have done.

I have a few questions that I suspect can be answered by “That’s just the way I prefer to do it.” or perhaps RTFM (or Wiki) but I’m going to ask anyway as I haven’t found answers yet. Feel free to point me to where these questions have been answered for the six millionth time if needed.

  1. People seem to be clamping their work just about anywhere on their wasteboard with clamps on all four sides as needed. I can see how that is needed if the workpiece is irregular but, I suspect that a lot of us initially start with boards that come straight off the scrap pile or big box store, that is, boards that are more or less rectangular. In that case, is there a reason that people don’t just create a “fence” on the X and Y axes somewhere (say the lower left) and use your favorite method to clamp the workpiece against those fences? It would seem that you could then register X and Y zero against the fence and just have to set Z and cut rather than having to re-zero X & Y to where you put the workpiece this time. What am I missing?

  2. Almost any of the tutorials that I’ve seen show Z zero being set at the top of the workpiece. Since the workpiece has more variation (presumably) than the top of the wasteboard, why wouldn’t you set zero to the top of the wasteboard and cut down to zero? It would seem that this would have an advantage when you are cutting all the way through the part without overly marring your wasteboard. Again, what am I missing?

  3. If you have a pattern of holes to be drilled (such as the grid of holes for a wasteboard using tee nuts or inserts) I’m assuming that you want to use an endmill that is smaller than the hole diameter and pocket the hole rather than using either a drill or endmill of the same diameter of the hole and try and go straight down. I suspect that doing that with an endmill is a good way to ruin one and doing that with a drill in your router would require a drill that could handle the router’s rpm range. I’m not sure that would be a special part or not but it seems likely that you would probably get a better cut with the endmilll anyway. I know that there are already pre-made files for this but I’m more interested in “why” at the moment rather than just following the canned script.

  1. that may work if you’re using a downcut endmill, but for an upcut the work will pull up. See https://wiki.shapeoko.com/index.php/Workholding and https://wiki.shapeoko.com/index.php/Endmills#Cut_direction

  2. top is easier, and if done wrong is less likely to cause problems. Bottom is appropriate and necessary for cuts which require it (joinery for example often requires it). See https://docs.carbide3d.com/tutorials/tutorial-homing/ and https://wiki.shapeoko.com/index.php/Designing_for_Fabrication

  3. Correct, sort of. Carbide Create doesn’t support drilling, but it’s not that bad to mill as a pocket. Drills which support the speed of a trim router are pricey and will pull the machine into a cut causing deflection. It’s that last problem which is why milling as a pocket is best. Some discussion of this at: https://wiki.shapeoko.com/index.php/Materials

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To add:

#1) There are clamping systems that essentially do this, but they either require high forces and a very rigid bed, like a thick piece of aluminum jig plate ( I have a number of projects posted here that use a cam-action system that works this way using a commercial sea-of-holes bedplate system), or the rail and clamp elements must provide some positive hold down.

Positive hold down can be done using a rail that has an undercut taper, so the top edge bites into the work a little, and clamps or wedges to drive into the rail that are similar, but the holding gear needs to be harder than the workpieces, and will mark the workpieces. I use tool steel (hardened and tempered O-1) hold-downs that work this way in manual machining when I need low-profile clearance, but if the work can’t tolerate the marking or the work is hard, other options need to be used.

#2: Ya, what he said.

#3: also, convenience. It is nice to minimize the number of tool changes. Also, as Will said, the drills can be expensive-- they need to support the speed and also need shanks sized for the collet you use-- and there is a limit to the hole size you can do due to speed and torque considerations, as well as deflection, and the limit is smaller than you might think. I usually use a tool chain that does support drilling, but, unless I have a reason, usually pocket holes. This has the added advantage of me not needing to stock of drills for every size hole. If I need a hole deeper than I can pocket, I will start it on the machine and finish with a drill press. This doesn’t happen often. For sizes too small to pocket, you can locate them with a vee bit (use a small circle such that when it is machined, it acts similarly to a center punch mark) and drill after the CNC work is done.

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Thank you @WillAdams. I appreciate your taking the time to explain “why.” as well as the pointers to the appropriate documentation. Reading things out of context doesn’t really penetrate for me unless I am looking for the answer to a specific question. I suspect that now, those documents you pointed me at will make a lot more sense.

Thank you @enl_public. I realize that these are the types of questions that can be answered in about 30 seconds if you are standing there with an apprentice next to the mill but take a lot more thought to try and explain over the medium of a computer forum.

From your answer, it sounds like you have a lot more experience than the majority of the people here on this forum. I appreciate your taking the time to help educate the rest of us who are coming to this from a non-machining background.

#1. What they said. Really just depends on preference - side clamping can distort the material, depends on what you’re doing.

#2 I have an opinion on. This one depends on what you’re trying to do. If you’re making parts that need a specific thickness you should probably set zero on the wasteboard. Then all the cuts are relative to a known surface, and you’ll get a known thickness. If you set zero on the top and do this, and you didn’t measure your material perfectly (or worse, forget to update it with the next piece of material) you’ll be cutting from the top reference. This can result in either cutting “too deep” and hitting the wasteboard or not cutting all the way through the material in other cases.

For engraving, you would generally use a top zero - the depth of cut is what really matters there (a few thou’ off is a big deal).

I almost always use a wasteboard zero.

#3 You got it. Drill bits are awful endmills, and endmills are awful drill bits. Even a center cutting endmill has trouble staying on center, which is a recipe for a broken endmill at the spindle speeds we use. A “drilling” option is really intended for spindles with slower speeds. Between the oversize, tapered hole, and the broken endmills, just pocket and don’t worry so much about it. That said, it does limit how small a hole you can make with the machine. The right thing to do then is to make a MARK with the CNC, and drill the hole with a handheld drill or drill press - right tool, right job.

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Thanks @mikep.

  1. I can see how sideways clamping pressure could distort the workpiece. I hadn’t thought of that.

  2. Sounds like there is no one true way. You have to take in to consideration what you are doing, the material, what the consequences of the error are should you make a mistake etc. Lots to learn here…I like it.

  3. I understand. I thought that that was going to be the case but wanted confirmation. Having said that, I just realized that when my machine gets here I won’t have any endmills that are smaller than 1/4". Ooops…Hello Amazon…

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I think you’ve got it now:

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Note that for smaller endmills you’ll probably want a smaller collet. We sell one for the DeWalt at: https://shop.carbide3d.com/collections/tools/products/precision-collet-and-nut-for-dewalt-dwp611 and Precise Bits sells an ER-style one for the DeWalt, and Elaire Corp. has precision collets for the DeWalt and Makita.

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Thanks @WillAdams. I ordered your 1/8" collet with my Shapeoko. Forgot about endmills though.

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