Screw Fixing with Directional Control?

thewools

Hi guys Ill try and explain what I need

I want to screw fix and object but require the object to be fixed in a certain direction every time in the assembly.

The part will have to be very tight when assembled (no vibration or slippage) but needs to easy to disassemble. I intend that the part can be tightened and untightened by hand if possible.

Can anyone guide me to how I can do this? Any help or feedback would be great...

DublinDilbert

Can you draw a rough diagram, doesn't have to show much detail, just a rough idea of what your trying to fix to what.

trad

Some type of a keyway or locating dowel / grub screw?

Turbulent Bill

trad wrote: »

Some type of a keyway or locating dowel / grub screw?

+1, one feature on the object for alignment (e.g., a peg or boss) and at least one screw for retention. You could also use at least two screws, which would combine the retention and alignment.

thewools

DublinDilbert wrote: »

Can you draw a rough diagram, doesn't have to show much detail, just a rough idea of what your trying to fix to what.

I will try and get something done and see can I upload it...

I want to draw somethin up soon in 3D CAD but looking at different fixing options before I start the design stages. I want the objects to be plastic but intial samples will be rough but functional using model making materials.

trad wrote: »

Some type of a keyway or locating dowel / grub screw?

Dont think a grub screw or locating dowel would work for my purpose...

trad

You could tell us roughly what you are trying to hold together. Plastics are not great for holding threads, you might have to fit metal threaded inserts.

thewools

trad wrote: »

You could tell us roughly what you are trying to hold together. Plastics are not great for holding threads, you might have to fit metal threaded inserts.

The parts will be plastic with a metal screw insert on the male side (top) and female on the base side... I dont want to give away my project publicly in the forum but will pm if anyone wants further details.

It's at the very initial stages at the moment and I'm not even sure if it will work but the idea is there and want to look into a few fixing techniques for starters.

I'll draw up something very basic now

thewools

Basic Drawing uploaded:

trad

If you use a fine pitch thread on the connecting bolt and with a lot of trial and error you can machine a fractions of a millimeter off the surface of the recieving section until the parts allign correctly, thats if you want to fix a stud in the top part.

Can you bore a clearance hole through the top part and just use a bolt to connect both parts and use allignment marks for assembly?

thewools

trad wrote: »

If you use a fine pitch thread on the connecting bolt and with a lot of trial and error you can machine a fractions of a millimeter off the surface of the recieving section until the parts allign correctly, thats if you want to fix a stud in the top part.

Can you bore a clearance hole through the top part and just use a bolt to connect both parts and use allignment marks for assembly?

Thanks for your reply

I agree this is how I would normally do something similar to this here at work but this concept which I want needs to be more aesthetically pleasing and simple for the end user.

Hence no grub screws, bolts etc

I want the end user to simply screw on and off the bottom part but still retaining the strength and direction required.

I was thinking a bit there - and maybe at the end of the screw head a small attachment might secure the direction. Ill draw somethin up again if I get the chance...

DublinDilbert

Does it have to screw on???

You could probably do something with a type of flat spring that would grip a feature on the other part, just like how a car mirror fits onto the metal button on the windscreen...

thewools

DublinDilbert wrote: »

Does it have to screw on???

You could probably do something with a type of flat spring that would grip a feature on the other part, just like how a car mirror fits onto the metal button on the windscreen...

Not too familar with this - does the part slide onto the assembly and lock into position? How can the part then be removed easily?

Turbulent Bill

thewools wrote: »

Thanks for your reply

I agree this is how I would normally do something similar to this here at work but this concept which I want needs to be more aesthetically pleasing and simple for the end user.

Hence no grub screws, bolts etc

I want the end user to simply screw on and off the bottom part but still retaining the strength and direction required.

I was thinking a bit there - and maybe at the end of the screw head a small attachment might secure the direction. Ill draw somethin up again if I get the chance...

If your just using a simple screw (like your sketch) it will be difficult to control both the mating force and the angular alignment at the same time. The tolerances in part lengths, screw positions etc. will mean that it's always a trade-off between these two requirements.

Given the objects are plastic, need good retention and position control, I'd look at a snap-fit design. There are thousands of examples available, with many of them having release options with push tabs etc.

Cheeble

Or how about a bayonet type fitting (like a light bulb)?

Cheeble-eers

-K2-

My suggestion is to use 2 dowel pins - one in the centre and one offset to achieve the alignment. You could use a screw for locking the two parts together (although this depends on axial and/or shear load on the joint).

But then again, I'm an EE :pac:

FarmerGreen

Thanks for boring a hole in my skull.
I thought , simple, mill dove tails on each part and click them together.
Its too expensive though.
If its an option of long or short, give the one of each.
On the other hand a bit more of a project deffinition would help.

Doc_Savage

this can be solved quite easily.... have the female part on a boss and tighten it against the male part then insert this into the female housing and you can have an interference fit of epoxy it in then the male part should unscrew leaving the female boss behind and maintaining your alignment every time it is put back together.

Figerty

Hi.

Your answer is not going to be a simple one, but here is my solution.

The part that is to in the direction.

Get the top part with the hole drilled in made as you have it. You can counterbore or countersink the top to all the bolt/screw head to have it flush with the top.

Drill ou the second part and tap a hole in the centre rather than having a screw thread coming out. A thread coming out will not be as accurate if you insert a bolt. Also, when you thread a hole the mating part will screw into it and tighten up. However, as the thread wear the part will rotate more, thereby loosing your direction requirement.

So my solution is drill and tap the main part. Clearance drill the top part for a bolt to match the thread.

Lastly, as someone mentioned, assemble the parts. and then drill and ream two holes for dowels both parts ensuring alignment. If you have to, you can loctite in the dowels in one part. This may be necessary if you aren't expieranced in the used of reamers.

Hope that helps