Hi everyone,
I am ordering parts for my first Primo build (25mm) and I have a question I hope someone can help me with regarding the tube sizing.
I will use a Bosch GFK600 ( I believe it’s called the “Bosch Colt” in the US) as I have one already. I noticed in the sizing guidelines that the tube lengths change based on the spindle, can anyone advise how to adjust the recommended tube sizes for this spindle or if there is a formula for working out the tube length - I guess it could be as simple as: desired working area x axis - width of
spindle = x-axis tube length? So if I order the wrong size tubes I guess it will just change the resulting working area?
What really worries me though is that I am already going for the minimum z-axis height and I am scared this will result in an unusable machine if I get the wrong length of tube. What do people think?
I don’t have a definitive answer, but I have some observations:
Relative to most work area sizes, the difference in tube length is relatively small. From the longest tubes in the calculator which use the DW660 to the shortest tubes when the “Full Range” is selected is only 9mm in the X and Y and only 2.5mm in the Z…and this is constant (i.e. does not change with workspace measurements). This small difference in sizes will make very little difference in the cutting ability of your machine.
To some extent, the mount for your GFK600 will impact required tubing length. How thick the band(s) are around the router and how far the router stands out from the tubing, where the mount positions the router nut relative to the bottom of the Z axis impacts the tubing length requiremen. Currently I’m not aware of a MPCNC mount for the GFK600, so you will just need to make guesstimates. And you are going to have to design or find a mount for this router. I think your router has a 70mm diameter, so a Dewalt DWP611 mount which is 69mm might work or be a design that only needs minor tweaking.
I assert that if you take the X and Y values produced by selecting the DW660 in the size calculator and add 6mm to each of them, and you take the Z value unaltered, you will have a machine that will have at least your specified workspace for any router up to 70mm (and assuming you have a mount with similar characteristics to the ones Ryan provides).
minimum z-axis height and I am scared this will result in an unusable machine if I get the wrong length of tube
If you are concerned about Z height, make the two Z axis tubes and lead screw somewhat longer, but keep the leg lengths the same. I’m talking about 25mm or more longer. If you decide you need a bit more height, all you have to do is swap in longer legs (which is very little tubing). And once you are sure you will not need any more height, the Z axis tubes and the lead screw can be trimmed (or not). The only downside to a longer Z axis (and keeping the legs lengths short) is a bit more mass on the Z axis.
Thanks a lot for taking the time to reply - it’s greatly appreciated. Your answer sounds logical and it’s what I would have probably done myself. I was just hoping to get the shop to cut the stainless steel tubes for me as I don’t have a decent cutting option myself - I suppose it might be a good excuse to buy something for that task now though.
You made me think - I just found a model for this router on Thingiverse.
thingiverse thing = 1870032
I’ll see if I can reverse engineer the width of that compared to the Dewalt holder and see what the difference is.- should give me a clue at least.
I see posters on this forum describe get their tubing cut by the people at the store/business. It seems to be fast, easy, usually creates a cleaner end, but it can be inaccurate. Fortunately the Primo can handle some inaccuracy with respect to the tube length. Getting the four legs the same length is very helpful but also not critical. For just shortening the Z axis at some future date, a simple inexpensive solution like a hacksaw with a decent blade will get the job done, but I’d hate to cut all the tubing that way. In a thread on this forum concerning shortening the Z axis, a couple of posters that had done this task claimed they were able to cut the tubing and lead screw without disassembling the Z axis.
I’ll see if I can reverse engineer the width of that compared to the Dewalt holder and see what the difference is.- should give me a clue at least.
I just pulled the models into Fusion 360. There is a 1mm difference between the model you reference for the Bosch Colt and a Dewalt DWP611…70mm vs 69mm. I used this Thingiverse model for the Dewalt reference. You can put a Burly mounting plate on a Primo and use the mount you reference, but it would be better to have a Primo mount.
For the z, the extra length sticks out the top, not critical unless you are building an enclosure over it. The nut traps are measured from the bottom. I left one of my burlys z about 3 times longer than I needed so I wouldn’t have to cut my lead screw. If you have any doubts at all, just leave them a little long.
I just assembled my Z axis a bit longer. I didn’t stick the tubes out the top. I still haven’t shortened my tubing to match my Z cutting height but will probably do so the next time I need to pull the Z axis.
Thanks guys for the tips and especially Robert - thanks for going that extra mile, really very kind of you to check that in Fusion for me. I’ll just order everything a little long and see how it goes.
Yeah, hacksawing steel is a thankless task! I would really rather avoid it.
Hopefully once I have it sorted I can provide the exact measurements and model for anyone else planning the same.
Great community by the way, looking forward to getting underway and talking to you guys more.
