Metric bolts and nuts confusement

Mostly Printed CNC - MPCNC Troubleshooting
#1

I printed more then half of the parts (25mm version), and starting the assembly. In the parts list there are M3.5 bolts, which are fine, and M8 bolts and nuts which I do not believe to fit :slight_smile:
Most of the holes in my parts are 4mm (3.5mm?) diameter, so that fits specification for M4 (M3.5?) bolts. But, the hexagonal holes/traps for nuts in these parts are 8mm, and that fits the specification for M5 nuts! I can’t find any M4 with 8mm heads… M3.5 uses 5.5mm head, M4 uses 7mm, and M5 uses 8mm…

What bolts / nuts are you actually using?
My first guess is to drill all the holes to M5 size, to utilize 8mm traps/holes but … did I undertood something wrong?

Regarding specified M8 bolts/nuts. They are huge! (8mm diameter of threaded part) I do not believe they will fit in any hole of the printed parts

#2

I used #6-32 bolts and nylocks and they seems to fit ok… Little snug required pliers to convince them to slide in on a couple parts. Most holes a reamed out with a drill just to make sure they were clean and the bolt had no issues sliding in.

#3

Hello, I don’t quite understand your issue. At least for me, the holes in the parts are ok for metric hardware.
Tell us which part is giving you trouble.

If you follow the assembly guide, when Ryan says to use “5/16-18 X 2.5” you should go to this link and see what’s the metric equivalent.

#4

Very interesting, so could you measure the sizes of your bolts and nuts? (sounds weird lol =) I mean measure hardware you use, not Your Hardware)) ), your thread diameter, and the size of the hex on the nut (size of wrench)

I’ve got two options which are both not good.

  1. If I go using M3.5 bolts - that will give me: Thread Diameter = 3.5mm, wrench size = 5.5mm (this is specification for metric M3.5 bolts). So, I will fit in the hole which is 3.5-4mm, but the nut will not be trapped by the 8mm wrench trap. (and the bad thing is also that there is no space to hold the nut by wrench)

  2. If I go using M5 bolts - that will give me: Thread Diameter = 5mm, wrench size = 8mm (this is specification for metric M5 bolts). So, I will not fit in the hole without drilling it from 4 to 5mm, but the wrench size of the M5 nut is exactly as printed nut traps.

#5

The nut holes are designed to fit the largest ones I could find.

These machines are being used everywhere in the world so it is easier to tighten bolts that don’t fit perfectly that to have others need to try and cut away plastic. This just came up in the forums yesterday as well. If you are having a hard time tightening the nuts either use needle nose pliers or try putting a small nail in there while you tighten it.

#6
#7

Undersood, thanks vicious1! I drilled some holes (where amount of plastic allowed) to 5mm, and 8 nuts are tightened there,but I will tighten others using some special tool (I think I will make some kind of bent foil adaptor to keep 7mm nut in 8mm trap.)

#8

P.S. Just for my interest - can anyone show me the hardware that fits 3.5-4mm holes and has 8mm wrench head size? Been to big hardware shop yesterday, where they have an Imperial hardware, and havent found anything that really differs from metric standards.

#9

The #6-32 hardware I ship with the kits fits it pretty good.

#10

I have just discovered this problem also, having purchased all Metric sized hardware. Yesterday I printed my Tool Holder and then the Nut Traps and thought I was going mad when I took an M4 screw and Nylock nut and test fitted them together - the M4 Nylock nut spins in the nut trap!

While the Parts Page lists both Imperial and the Metric equivalent, in this case I don’t think it works. M4 nuts are 7mm wide (across flats) but SAE #6 nuts are 5/16" (~8mm, across flats) which is what the nut traps are designed for. For parts like the Rollers, Corners etc, it isn’t a big deal as you can access the nut to hold it or jam something in to stop it spinning while you tighten it. With the Nut Trap, you can’t access it while tightening. If you jam something in there and it falls out, how do you ever undo a spinning Nylock inside a tube? Drilling it out the screw head would be the only option.

I am thinking I will remix the Nut Trap and Tool Holder to fit M4 hardware to solve my problem. I may have to do that anyway once I get my router and design a mount for it (the mounting holes on the Tool Holder are all the same size, suit #6 hardware).

Can we get a note put beside those parts in the parts list please (both the printed parts and hardware)? This may help others in Metric countries understand the pros and cons of substituting Metric for Imperial. Maybe even a sticky in this sub-forum?

I’m not trying to have a go at Ryan, the design or anyone, just wanting to highlight a problem.

#11

There is a parametric nut trap on thingiverse if you are having issues. Pretty sure geodave made it.

I assume people have just been gluing them in like the tool holder nuts. I will double check but I think it says this in the instructions. I glue in the nut trap nuts and tool holder nuts, I saw this in the instructions yesterday but I will make sure it is in both places.

Sorry it a hassle for you guys, no has really mentioned it up until now.

#12
#13

Sorry for late reply, had a busy weekend and then back to work.

Thanks for your reply Ryan/@viscious1 (I never know what name to use!).

My solution to this in the short term has been to find some #6 nuts from my work and drill and tap them for M4. I did 4 of them to use for the Nut Traps and Tool Holder. I can still glue them in too.

I checked the assembly instructions for the Z-Axis and yes it says to use glue. What glue do you use?

#14

Depends what is closest, I am lazy. Either superglue/cyanoacrylate or threadlocker…so lazy

#15

Hi all, I’m getting the same problem as Jono with the Nyloc nuts spinning in place on the metric version. I’ve solved it with this: http://www.thingiverse.com/thing:1904014 “M4 Nut Encasement”.

Basically, it’s a little casing that holds an M4 nut and makes it fit closely into the hex cavities, where the nut would otherwise spin. They need printing with a fine nozzle because the walls are so thin. I’ve posted the OpenSCAD file - it’s very simple; they’d probably work better with M3.5, so feel free to experiment.

Hope this helps!

MBEF

#16

For the Z axis pipe try this for Metric M4 nuts

http://www.thingiverse.com/thing:1872142

Full disclosure - I designed this.

Rest of the M4 nuts I didn’t really have any problems with.

#17

Hot glue is another temporary solution.

#18

@Fermata Brilliant - thanks for the link, I was wondering how that was going to go. Yep, the other nuts aren’t too bad - but I managed to break a couple of the pieces trying to get leverage against the nut, and I didn’t want to break any more. Another simpler solution was just to put an ordinary (non-Nyloc) nut on first and use slightly longer bolts, but the nut-holder looks more refined.

@Vicious1 Yep glue, good solution. And, we can do that as well!