Custom build here - have some questions

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DRobs86
Posts: 148
Joined: Fri Jun 05, 2015 4:19 am

Custom build here - have some questions

Post by DRobs86 » Wed Jun 10, 2015 4:45 am

Hello everyone.

I don't have a Shapeoko but I thought I'd try to contribute and learn from you all here.

First, I'm looking for a formula for cutting force calculations. I'm sure the formula is full of variables, but I'd like to create a spreadsheet to do this. Is this ( http://zero-divide.net/index.php?page=fswizard ) calculator good? I'm kind of using the SO machines as a yardstick for my custom machine. What kind of cutting force would one expect to make with the SO 1, 2, and 3 without stalling or seriously deflecting the machine?

I ended up using a DW660 on my machine. It seems reasonably powerful (clean cuts on MDF so far at about 600mm/m at 13 mm depth with a four flute carbine 1/8th endmill), but I feel like for a little more (or less) money I could have gotten a real router. Specifically, I'm curious if anyone has used the Skil 1817RT. It's fixed at 25k RPM and has 1.75HP vs. the DW660's 0.8HP at 30K RPM. Amazon has factory reconditioned 1817RTs for under $50 bucks. Is the Skil worth a look? Any experience with it in the community?

Here's a pic of what I carved tonight. This is with a 4 flute 1/8th endmill. The top initials were run at about 4mm at about 500mm/m and the bottom initials were run at the same depth but only about 250mm/m.
Image

Finally, I want to check the validity of what the wiki claims for MDF milling settings: http://www.shapeoko.com/wiki/index.php/Materials#MDF
Those bottom two reports look reasonable but I'm dubious of the first one (the one that doesn't report cut depth). 100 IPM is 2540mm/m. It's kind of hard to judge the reasonability of that figure without a depth setting. I messed around and ran some gcode without setting everything up correctly first and ended up 6 to 10mm in the material doing a G0 at 4000mm/m (with the spindle on) and it just plowed the MDF and busted chunks out of it. Is a 100 IPM cut on mdf really possible at at any kind of significant depth without tearing it?

Thanks in advance for the info!

clockit
Posts: 319
Joined: Sun Nov 16, 2014 11:05 pm
Location: California, MO

Re: Custom build here - have some questions

Post by clockit » Wed Jun 10, 2015 8:51 am

I know nothing about milling metal so I can't address part 1 but I will try to convey my experience with my SO2. Material feed rates can be hard to compare, for example, I push my Makita more than twice as fast you do your Dewalt, but, I'm not taking 1/2" cuts each pass, with a 2 flute 1/8" endmill. However, I haven't tried to push mine that fast that deep.

However, I think my feed rate stay more in line with what the machine was intended to do. My results are incredible, at least I think so, and I can repeat it over and over. I have a decent work area, I know I paid A LOT less per sq. in. of work surface than those with other brand of machines. However, I also know that it's an entry level machine that was presented to the hobbyist at an incredibly reasonable rate. I have a scroll saw that I paid more for than my SO2.

It is know that there is a little flex in the X, but you can do work arounds to stiffen it, same with Y when you start expanding it from stock configuration. Depending on your Z set up there can be some flex... but I've never tried another mill, I have nothing to compare it too, and it wouldn't really be fair to do that with a machine that you paid 5x more for. It also really depends what you are producing, if you're making plaques with script on it does it really matter if something is 1/32" off, would anyone notice it? Crank it up and let her fly... however, if your cutting something demanding a certain degree of precision, slow it down.

And that's where I run into an issue with the Skil router and it's fixed speed. I routinely adjust the speed on my Makita depending on what I'm cutting. I actually had an issue once with oak that I wasn't spinning it fast enough and it was 'burning' the wood, the bit was getting hot... both are not a good thing, lol... opened her up a little, actually a lot, and no a problem. So, with the Skil you're going to be locked where you are and just have to hope that it's close enough...
Shapeoko 2, Full Kit #7071, Makita RT0701C Router, 1000 x 1000 upgrade, Acme Z Axis w/Nema 17 Belt Drive

WillAdams
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Custom build here - have some questions

Post by WillAdams » Wed Jun 10, 2015 10:38 am

DRobs86 wrote:Finally, I want to check the validity of what the wiki claims for MDF milling settings: http://www.shapeoko.com/wiki/index.php/Materials#MDF
Those bottom two reports look reasonable but I'm dubious of the first one (the one that doesn't report cut depth). 100 IPM is 2540mm/m. It's kind of hard to judge the reasonability of that figure without a depth setting. I messed around and ran some gcode without setting everything up correctly first and ended up 6 to 10mm in the material doing a G0 at 4000mm/m (with the spindle on) and it just plowed the MDF and busted chunks out of it. Is a 100 IPM cut on mdf really possible at at any kind of significant depth without tearing it?
Take it up w/ the people who posted the data which was copied. Best is to use the values on the wiki as a starting point for: http://www.precisebits.com/tutorials/ca ... speeds.htm

Rather than a spreadsheet, my suggestion would be to get G-Wizard and be done w/ it.

Get MeshCAM as well, since the two are integrated.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

DRobs86
Posts: 148
Joined: Fri Jun 05, 2015 4:19 am

Re: Custom build here - have some questions

Post by DRobs86 » Fri Jun 12, 2015 4:03 am

Thanks for the replies.

Have their been any reports on tool longevity using a speed controller on the DW660? I've followed this forum a bit and have read some concerns that the DW660 won't cool properly if turned below 30k rpm. I'll probably end up working with the DW660 for a while (May try the Skil on a future machine), but I'd also be interested to know the general case. Do tools built for fixed RPM survive variable speed control nearly as long as they would if just run at the intended speed?

Will:
G Wizard looks pricey for my blood, but thanks for bringing it up. I'm going to look into the science of cutting force calculations a bit and I'll share if I find anything useful. The main goal here is to establish a maximum cutting force figure that my machine is capable of with no deflection artifacts in the workpiece. I think from there I could translate that into other materials or cuts.

Thanks.

WillAdams
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Re: Custom build here - have some questions

Post by WillAdams » Fri Jun 12, 2015 10:43 am

For a hobbyist, G-Wizard is a one-time payment of $69 or so, then one gets the calculations for a 1HP spindle at the G-Wizard Lite level in perpetuity, which is a nice compromise on typical cloud pricing schemes.

It just has to save one from a couple of broken bits or extend tooling life a bit to pay for itself. It’s a really good value, and one which I’ve been seriously tempted by.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

Hans
Posts: 290
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Location: Connecticut, USA

Re: Custom build here - have some questions

Post by Hans » Fri Jun 12, 2015 1:31 pm

The S1 and S2 both give good finish passes at around 1 pound cutting force per FSWizard. Roughing passes, maybe up to 10 pounds depending on how aggressive you want to be. Creator Edward has posted an aluminum milling video with the S3 with good finish and parameters that FSWizard spits out about 4 pounds for.

I don't think you'll stall a DW660 with cuts under 10 pounds, at least I haven't stalled mine. It might be doable with a big endmill and a hard material, but you'll definitely run into deflection problems long before running out of oomph.

With a more rigid, production-oriented machine huge cuts are possible in MDF. The only limit is your machine.
Shapeoko #1,123

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