[THKL]

Hiho,

I'm currently currently converting the Momus 2.0 plans to metric sizes and meanwhile model my work in Sketchup to verify everything. While I'm at it, I added some changes to better suit component availibility in europe.
While doing so, I'm thinking why the bearing blocks (those carrying two bearings - parts 14/15) and the Z motor mount (parts 20/21) are held into place with studs that need tapping.
At least in my metric model I can't see any clearance reasons for this design decision (might be different in imperial sizes - for instance I don't have to use modified bolt heads for the carriage assembly which are definately required for imperial).
So is that design decision based on strength differences in the joints?
Could it be substituted with bolts or studs with a nut on each side of the stud?
Since I really hate tapping holes, that would greatly simplify the fabrication for me...

Thanks for the feedback,
Thorsten

[vtxstar]

Thorsten, your questions are valid.

Regarding the parts in question, the studs in part 21 would be fixed with Loctite, pass through part 16, then 20, and be secured with washers, locks, and nuts. I see no reason that two bolts of the proper length could not be inserted into 20, 16, then thread into 21. Either way, 21 would be threaded to allow the clamping action...unless you passed through and used nuts also.

On the other hand, the threaded rods cut to length and employed as studs, are cheaper than bolts... a design goal to be sure. Rather than 1/4-20, a Euro version could use 6 x 1mm or 1.25mm pitch threaded rod...if available.

That size would still allow sufficient part surface area for a secure clamp.

Don't like threading holes?
How about my caveman method of using a hacksaw for all the parts so far?
I have yet to buy any stock as I am sourcing from my junk pile... and finish the hand cut parts on my mini-mill.

-=Doug

[THKL]

The argument for price might be another reasoning I didn't think of.
I personally would like to remove the threading alltogether (at least for the most parts) und use bolts and nuts for clamping or studs with a nut on both sides.

Studs with nuts on both sides might be cheaper for the general public, but through a friend I have my ways of sourcing all the screws/bolts/nuts through one of Germany's largest distributors at their own buying prices - all those parts are a few cents each (if at all), so going down th bolt route is actually less hassle for me and won't really affect the price...

[cgodwin]

I'm nearly done with my machine, and if I was going to do it again I would replace the threaded rod almost everywhere. It doesn't is weaker than a bolt and a ton of extra work for no apparent reason. The cost savings certainly aren't worth it. Taking a quick look at my machine, I only see 2 places where using a bolt would require a design change.

[momus_cnc]

Correct that in most places the studs can be replaced with bolts & nuts. My rationale in designing it with studs was for several reasons:

1. I tend to be a little on the frugal side, and it was cheaper to cut studs from threaded rod.

2. I wanted to keep the mass of the gantry as low as possible, as I was anticipating cutting things like foam and wanted to be able to keep the acceleration/deceleration as high as possible. This might reveal that I tend to be a little obsessive (in case nothing else already gave it away.)

3. Aesthetics. To me it just looks better. It looks slightly less, ummm...bolted together.

4. I'll admit to actually enjoying tapping holes in aluminum. It makes me feel like a real machinist.

I have actually thought about this issue, and if I ever get around to a Version 3 of the machine, this might be something I change. The amount of time saved by using bolts might offset my original reasons listed above.

-Bob

[swkusr]

Hi,

I'm in the process of laying out the locations on the metal pieces. After reading this thread , I'm inclined to give the bolt & nuts method a try.

Can you share the 2 locations where using a bolt would require a design change ? Would Loctite still need to be applied to the bolts ?

Thanks.

-Hock

[THKL]

Well, interesting to hear about the original intentions.
It's always nice to see the details that really just show up when you are trying to change things - tells me how much time and thought you really invested into the project!

While doing my conversion weight reduction was not really high on my priority list - for instance I opted for a symmetric design of the upper and lower carriage "beams" and I changed the width of the steel, the bearings are riding on, to 8mm so that the bearings always fully touch it.

If aesthetics is one of the main goals, I would rather go with studs that have a self-locking nut on both sides - that creates a clean symmetric look and you don't have to worry about sizes, because you can just cut them to fit (even afterwards)...

That aside, I like to use bolts because they just ease the production process - while feeling as a machinist is a nice bonus, I would not only think about the time-savings, but about the risk of breaking a part which is considerably going up since most of the builders won't be too familiar with tapping.
Another thing to consider when using studs and threads is that not everyone is going to perfectly cut them and since aluminium is such a soft metal things can easily become slanted - being either because of the thread itself or because of not perfectly threading the stud in which then re-cuts the thread...

Just my 2 cents
Thorsten

[vtxstar]

I'll admit to actually enjoying tapping holes in aluminum. It makes me feel like a real machinist.

As do I Bob! Using my mini-mill and a tap guide helps a lot. I cannot recall breaking a tap while using a tap guide and the mill.

Even though the goal is a machine to do the bidding of the Gcode I write, having some 'skin in the game' is part of the process to me.

-=Doug