Pulling my hair out trying to find components for a jig; adjustment screw arrangement

[nadsab]

Hi,

I am pulling my hair out - trying to find some components for a jig I am designing and am having trouble finding it – no company i have contacted by phone today has what I am looking for - so I will describe what I am looking for and maybe someone can give me some advice as to who I can call to buy it – or at least tell me what to call it -what the mechanism is commonly known as.

Anyone know what a drafting compass is? With the thumb wheel in the middle which when turning spreads the legs of the compass apart?

That is what I am looking for- a threaded rod, with both left and right hand threads, a thumb wheel in the middle and cross dowels, or dowel nuts or trunnion nuts on the end.

I am trying to put together a version larger than a compass though – either 8 or 10 Gage screws – I could settle for ¼ inch but that is a bit large for me – and hopefully a precision screw like maybe 80 or 60 threads per inch if possible (would accept as low as 32 tpi if I have to though). I have called all the adjustment screw specialists i could find.

All I need, are those three parts – the middle thumb wheel, the threaded rod – technically known as “equal thread length rods – right and left hand threaded”, and the cross dowels, or dowel nuts or trunnion nuts to go on the end.

I can find equal thread length rod but only in 1/4 20 at Mc masters, and I can find cross dowels in same but I am looking for something more precision...

I am trying to build a jig, and on this jig, I need to spread two aluminium plates apart and provide between 10 to 45 degree angle between the two plates - is there a better way to do this with low cost (I am talking about under 25 bucks) manual components?


Anyone have any suggestions where I can find this?

Thanks.

[Magnum164]

Not sure how to help you, but as far as drafting compasses. Yep. Used them a lot, a picture may help others.
Alvin Quick Action Standard Drawing Set Q407KA -

I am not picturing what you are trying to do though.

[lkenney]

How apout using a screw driven sliding wedge to spread your plates. I am assuming that the plates are rotating on a pins or screws at one end A slot in each plate that captures a steel dowel on the wedge would allow precise adjustment with a single screw.
Lowell

[nadsab]

Thanks much for the idea - I think I have decided on going with a worm drive - more involved than originally planned but it will work OK,

[nadsab]

lkenney,

Actually that sounds like a much better idea than my worm gear idea, much simpler and cost effective. Yes - the plates are rotating on pins if I use this kind of design...

I am trying to visualize what you are saying though...

Are you saying to use the steel dowel as a wedge and push the dowel up toward the inside corner of the two plates? And have the dowel ends resting in slots in each plate on the inside corner side? And situate the adjustment screw perpendicular to the dowel to push the dowel towards the inside corner?

If that is what you are saying it might work, the only other issue is that once in position those two plates need to be locked in to the angle after adjusting...I can't have any movement between the 2 plates...

That brings me to another question - is there such a thing as a fine adjustment hinge?

[mcphill]

Not sure this is exactly what you were looking for, but I think it could get you going in the right direction...

McMaster-Carr

[nadsab]

Yeah I was thinking about that a while ago - can't get the degree of precision I need with a turn buckle though - they only make them in the coarser threads. Was hoping to do this with an adjustment screw or some other means.

[mcphill]

Then fill the threads with JBWeld and tap it with a fine pitch thread, and buy the corresponding threaded rod... Won't cost any more. Put lock nuts on it as well, and you can limit travel significantly. That the play in fine pitch threads is still too much, do something like this for zero backlash:

Making Acetal leadscrew nuts the easy way - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

[adprinter]

I had a need for a precision adjustment (aiming laser beams for screen printing). What I designed, gave me 3 axis of movement. The key element of the design, utilized dowel pins, which were turned down to a smaller diameter at one end, and a groove cut into the small end to accomodate a snap ring. The opposite end, was drilled and tapped perpendicular to the longitude of the dowel pin. A second dowel pin was drilled to accommodate the diameter of the threaded rod (but NOT threaded, the threaded rod simply rotated freely inside this second dowel pin). Two of these pins were used for each axis of movement in my application.
The aluminum plates were drilled to a slightly loose fit for the diameter of the small end of the dowels, the pins were inserted into this hole, and the snap ring was installed on the back side of the aluminum plate to secure the pin. The same was repeated for the second pin into the second aluminum plate. The two aluminum plates featured a simple hinge type bolt which secured one plate to the other.
I used a single threaded rod, which featured a knurled knob secured to one end using lock nuts on either side of the knob. A locknut was threaded onto this rod, and adjusted almost all the way up to the back side of the knob assembly. This rod was then inserted into the second dowel pin (the NON-threaded pin) and a locknut was then threaded onto the rod, and adjusted all the way up the rod until in contacted the bottom of the second (NON-threaded) dowel pin, and was then threaded into the first dowel pin. A locknuts which were installed before, and after the second dowel pin, were tightened just against the dowel pin to allow the threaded rod to be rotated, yet eliminate as much back lash as possible.

Since the dowels are allowed to rotate freely within the holes of the aluminum plates, rotating the knurled knob of the threaded rod clockwise resulted in the two dowel pins being drawn closer together (and the aluminum plates acting as a hinge mechanism, closed). Turning the knob counter clockwise resulted in the two dowel pins being pushed apart from each other (and the aluminum plates acting as a hinge mechanism, opened).
I am new to CNCZone, and do not yet know how to go about uploading files to the site. So I have tried to describe in words, what could easily be communicated with pictures.
The above procedure works very well, even though it sounds impossible because of the arc of movement in a hinged assembly application- since a straight line shaft (the threaded rod) is used. The feature which makes this work, is the fact that the dowels are allowed to rotate within the mounting holes.
This does present some binding issues, however for small degrees of movement works fine. A person could conceivable add ball bearings to the holes of the aluminum plates, and insert the dowels into the ball bearing which would result in a more fluid motion. However, in my application, I wanted the aluminum plates to remain secure at the postion they were moved to, once rotation of the knob is stopped. Had the dowels been mounted using ball bearings, the whole assembly would probably be very sensitive to vibrations, causing them to move. Hope this helps. It was quite a challenge for me to design this system.