Dovetails and Spring Plungers

[Cartierusm]

I'm trying to make an adjustable plate for a tripod and I'm going to use the standard 60 degree dovetails. The dovetail needs to fit smooth with very little if no play at all. I am an accomplished machinist but never having made dovetails before I'm not sure how easy it is to get a tight fit that moves easy. Or since most machines use a gib is there always a need to have an adjustment. This is not machinery that's being made so the unit won't be moving all day long. I do have anodizing setup and it will be anodized for wear protection.

Now having said that, in my mind there will probably be a need for some kind of ajustment to make the dovetails fit nice. I'd prefer if it didn't use gibs and grease. So what I'm asking is I found this on Kipps website, it's called a spring plunger and I wondering if it could be used as an adjustment, coming in from the side and use the ball as a ball bearing to keep tension on the dovetail but still move easily.

Here is the web addy and a pic.
http://www.kipp.com/cms/wm?catId=231...xtFamily=false

[Geof]

It will work but the ball makes contact on a very small area, actually unless the metal it contacts deforms the area is infinitesimally small. Aluminum will deform even when it is anodized, and eventually the ball will create a score mark and may tend to gall up.

Possibly a better approach would be to put a Delrin plastic plug ahead of the ball so the ball presses against the plastic with the plastic being the part that slides on the anodized surface.

[Cartierusm]

In that case there would be no need for the spring plunger, just drill a hole, thread and put a plug that's been cut at the end at 60 degrees and follow with a set screw, oh and maybe a small spring for tension.

[LeeWay]

They make those spring plungers with all sorts of different ball materials. McMaster Carr carries them with Delrin, nylon, brass, etc. Just search for spring plungers.

[Cartierusm]

I've seen those, but as Geof already said the amount it plunges in is real small .03" for a 1/4-20 one. With my idea I have a lot more surface area and more control.

[Mcgyver]

Originally Posted by Cartierusm I'm trying to make an adjustable plate for a tripod and I'm going to use the standard 60 degree dovetails. The dovetail needs to fit smooth with very little if no play at all. I am an accomplished machinist but never having made dovetails before I'm not sure how easy it is to get a tight fit that moves easy. Or since most machines use a gib is there always a need to have an adjustment. This is not machinery that's being made so the unit won't be moving all day long. I do have anodizing setup and it will be anodized for wear protection.

making a very fine fit with a dovetail is no different than other close fit you've machined - you just have to work carefully so there is minimal clearance. that means careful measurement and the trick with dovetails is to use something like ground pins to measure them. work out the math - or formulas are a google away and then then you can mill down a an exact fit, say a thou clearance - pics below illustrate this.

working carefully can make them to where they slide easily but won't fall out under their own weight.....but...if its for motion (as opposed to very occasional adjustments, I wouldn't make one without a gib. Gibs are simple to make, they don't have to be fancy tapered ones, just a flat piece of material with the angles milled on (you used the actual dovetail to hold the gib to mill the angle on).

Also, AL wouldn't be my first choice, esp if there is a lot of motion - you say its not moving all day but also that its anodized for wear which suggest some amount of motion

getting it the right distance from the edge (this is a small adjustment dovetail for a cut knurling tool i made)



adjustable parallel to measure inside



outside is straightforward

[John Welden]

You could make one side of the dovetail out of delrin and the other side out of aluminum. It would slide well if you did a nice job. It's just for a camera so its not like you need super precision and fancy adjustment.

If you CNC it you can just comp it until you like the fit. No need to measure anything. Cut the aluminum side first.



If it were me I'd just buy a linear bearing set up. Perfect slop free motion with almost zero friction. It would be more compact and weigh less.

Dovetails are old school.

[Cartierusm]

Dovetails are more compact. The smallest linear setup I've seen is 1/4" round, which makes the bearing 1/2" diameter. That's not very compact and this thing needs to be as compact as possible and light. I've also looked at bronze busing for the linear slide, same thing. I've done a full CAD drawing as I am CNCing it and the dovetails are way more compact and cheaper to make too. But I'm open to suggestions.

[John Welden]

Originally Posted by Cartierusm Dovetails are more compact. The smallest linear setup I've seen is 1/4" round, which makes the bearing 1/2" diameter. That's not very compact and this thing needs to be as compact as possible and light. I've also looked at bronze busing for the linear slide, same thing. I've done a full CAD drawing as I am CNCing it and the dovetails are way more compact and cheaper to make too. But I'm open to suggestions.

Mcmaster has a precision guide blocks a rails that are only 2mm tall (.08") 15lb load capacity. http://www.mcmaster.com/#catalog/115/1081/=323b2h When I said linear bearing, I was talking about these. Kind of a generic name for that sort of thing.

I'd highly recommend them over dovetails for what you're doing. They just work so damn well and the feel is perfect.

[cad01]

WOW!!! I didn't know they made them that small. Pretty cool but $87 makes for one expensive tripod. I guess it depends on what it is used for and how deep the pockets are.

[Mcgyver]

lots of engineering considerations would go into a selection of dovetail/box/linear bearing, and one is hardly universally better than another. not knowing the application makes it hard to make a sensible recomendation, for example, they would not have worked in the photo sample i put up. Interesting though to know they are available in such small sizes

[Cartierusm]

WOW doesn't cover it HOLY S*** is more like it. That's freakin' amazing. I had no idea they made them that small, pretty wild. I don't think it's in my budget though, but COOL none the less.