Conduit for best rigidity

So I just received my kit and I need to buy the conduit. What’s the best conduit I can use and what size. Basically when I go to the metal shop I need to know what to ask them for. I’m hoping to be able to cut steel down the road when I replace the plastic with metal. Also what’s the best spindle for me? Thanks

Depends on which kit you got.

They use either common (In North America) 3/4" conduit, which you can buy at any home improvement store. These don’t typically come with material test sheets, so… You get what you get. It’s 23.5mm OD tube, though, so whatever works from there should be fine.

Printed parts for 3/4" conduit have the parts marked with a “C”

Or they can use 1" OD (25.4mm) tubing. In this case, you have some choices. You can go with DOM mild steel tubing, usually has a weld seam on it, but overall smooth. Alternately, at a higher cost you can use stainless steel tube. These do come in a variety of thicknesses, but 0.065" wall is pretty normal. Printed parts will be marked with a “J”

Or they can use 25mm OD tube. This has similar choices available. These printed parts will be marked atih an “F”

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In one short question you hit on three major topics. These topics have been covered multiple times on this forum with dozens or even hundreds of posts. Unfortunately, there is a wide variation in MPCNC builds, so a lot of the data is soft. Some of my takeaways from reading these topics:

  • The larger the diameter of the tubing, the stiffer it will be given the same wall thickness. The 25.4mm version will be the stiffest of the three available MPCNC versions.
  • Some testing has found that DOM tubing is a bit stiffer than stainless steel tubing (of the same wall thickness), but DOM tubing rusts and therefore must be treated with something like paste wax.
  • Thicker tubing is not automatically better. Thicker is heavier and tends to bow downward. For the edge pieces, this can be addressed using mid-span supports, but not the crosspieces. In addition, thicker crosspieces are heavier and therefore impact the ability to accelerate. Picking the right tubing is a balancing act. For most machines 0.065" walls seems to be the sweet spot.
  • If you are looking at cutting metal and are going the router route, then the Dewalt DWP611 or the Makita RT0701C seems to be the sweet spot between power and weight.
  • If you are looking at spindles, the smaller 300-watt and 500-watt models will be underpowered compared to the mentioned routers, but 1.5KW units will add notable weight compared to the routers.
  • Cutting metal with the MPCNC is hard(er). I’ve only seen one or two topics on this forum where steel has been cut. Keep your working area small if this is your long-term goal.
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You have a link to this one? I thought it was the opposite.

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Thanks for that. I guess my issue with DOM is that mine came in with a bend in it. The SS I ordered to replace it is perfectly straight.

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And to be fair, we have one test with two specific batches of tubing, and we are using that to generalize about the stiffness of DOM over SS.

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True. But that’s a better distribution than most political polls :smiley:


That reminds me. I put my primo back together and ordered some coated endmills…time to go try steel on THIS one.

Ok so i have settled on .065 1in SS Tubing now before i can buy the tubing i need to know what spindle to get should i go with a spindle or a router? I want to cut steel, and also with the spindle cant you control the speed with gcode?

There are a number of topics on getting spindles to interface with CNC control boards. The issue is that most VFDs use 0 - 10V as input for spindle RPM, so you somehow have to take a PWM signal from your board (3.3V, 5.0V or 12V), and figure out how to generate 0 to 10V signals. I’ve seen special boards and divider circuits used, but this I don’t see one common or right way to make it happen. It is doable, but expect to put some work into research and experimentation to make it happen.

As for spindle vs. router, there is not much comparison data on this forum between the two. There are very few matching spindles to the 1.25 hp trim routers like the Makita and Dewalt. Most spindles are either smaller (300 watts to 500 watts) and therefore underpowered, or larger (1.5Kw or 2.2Kw) and therefore heavier. More mass at the core impacts acceleration and therefore feedrates. A router of 1.25 hp would be similar in power to a 1Kw spindle (and probably similar weight), but I don’t see spindles near 1Kw being sold.

As for steel, I’ve seen it mentioned a time or two on the forum, but it is not common. I would expect a lot of experimentation on your part to get good settings to cut mild steel.


So from the sounds of it you would recommend going the non spindle route. So what would be the best router to get

The two big-name router choices are the Dewalt DWP 611 and the Makita RT0701C (any 700 series). Of the two, I would recommend the Makita because has had significantly lower minimum RPM, and you are going to want lower RPMs for metal. In addition to the Makita there are clones that are worth considering. Avoid cheap Makita clones due to unknowns about the speed control electronics, but you can consider:

  • Carbide 3D router - this router is a bit cheaper than Makita and comes with precision collets. You will almost certainly want to purchase a 1/8" collet if you purchase the Makita. The 1/8" collet is available several places including the V1 store.
  • Carbide ER-11 Compact Router - A more expensive option, but it accepts ER11 collets, which are easier to find and provide more variation in size of bits accepted.
  • The router in this topic. This is another Makita clone that accepts ER11 collets, and is more expensive. What intrigued me was the description in the video of the upgraded bearings. In theory better bearings should provide less runout, but for all I know, the other routers I list might have similar bearings.

Note the routers that accept ER collets were first mentioned on the forum yesterday, so there is no data on their performance.

As for spindle vs. router, I don’t have a solid recommendation. I’ve only ever used a router, and I’ve never
tried to cut steel. There is very little data on the forum comparing larger spindle performance with router performance. What I can say is that there are a lot of success stories on the forum using the routers for materials up to aluminum.

I’m mainly going to be cutting copper, aluminum and acrylic. So it sounds like the makitia is the way to go?

Wait, what happened to DW660?

I have had mixed results with steel using the DW660. The machine is not like the huge beefy machines that feed with huge forces and large torques at low speed. You could install a powerful, high-torque spindle but you probably won’t be able to use its true strength, so it’s a bit of a waste. Lots of smaller bites is the name of the game, the downside being that heat is much more of an issue. I never got around to using coolant for steel, but my thought was that coolant should allow going slower with smaller chips and lower loads without toasting the bits right away.

I’ve never done steel, so your experience might provide a better answer for Jededish. I did not mention the DW660 because of its lack of a speed control. From what I’ve gleamed, cutting metal benefits from slower RPMs, and the DW660 as a fixed, 30,000 RPM. You can put an external speed control on the DW660, but you lose a lot of torque at lower RPMs, plus there is no feedback loop, so the RPM will vary somewhat as the load on the bit changes.

Ah, ok. Well as far as that goes, you are correct. DW660 does not have speed control and as I understand it, cutting metal generally benefits from lower RPMs, higher torque, and larger chips. But stiffness under very high loads is not MPCNC’s strong suit, so compromises have to be made.

Personally, I purchased the Carbide 3D router. I believed it to be comparable to the Makita, and even after taking the shipping into consideration, I saved over $30 compared to purchasing the Makita and a 1/8" collet. A lot of people on the forum use the Makita, and are very happy.

I don’t know what you plan on replacing, but the primo is plenty capable IF you pay attention during your plan, build and setup, and aren’t trying to do ‘too big’ pieces. My experience stops at about 6x6, but I know that’s not the upper limit.

The makita is capable of lower rpms right out is the box, 10k or so vs the dewalt 16k. Also sits closer to the core than even the 660 now (more rigid) if I understood Ryan correctly. I’m thinking about getting one even though I’m pretty happy with my 611, since most steel cutter manufacturers recommend rpms between 8k amd 14k for smaller tooling like 1/8.
On the other hand, other folks with desktop machines actually cutting steel subscribe to the “letter rip, tater chip” school. Moderate DOC (30-100 thou) light stepover (10-12%) and just go at it. I’ll try that method next.

Here’s a new one…