Alignment Pins

[Chazz]

I have been using doweling pins as my alignment pins for some time now. However, I have come to find out that they are not working as well as I presumed. There are a couple of issues that have hurt my projects.

1) In time, they seem to shrink and be smaller than they are supposed to be. My 1/4" dowels wiggle in 1/4" holes. I have found that this can be overcome by soaking them in really hot water for a time, then letting them air dry. It only works for a few days though before they shrink again.

2) When I had two pins in a job -- 18" apart, the material was still able to shift with the material flat on the base board and the pins in place. Again, I was using 1/4" pins... possibly part of the problem.

In my current job (the one with an 18" spread between the pins), I wound up with a 1/16" difference on something that I cut from the two sides. I quadruple checked the drawings (and allowed some time to cool off from the frustration of it) and they seem correct.

Thoughts?

Thanks,
Chazz

[Brady Watson]

Ditch the wood and go metal. Get on McMaster and pick whatever material you want as a durable dowel material.

I've done 8/32 wood t-nuts, countersunk from the back of the 'jig board', which is secured to the bed. Then machine screws hold the parts down from the top. You might have to play with depth and screw length, but it usually isn't too bad. They are small enough to not need too much slop to fit everywhere & the fine thread gives you lots of leeway for how much torque you want to apply.

-B

[donek]

I use clamps to mount stops to my table. I do have room to clamp things though. The program I created to do so is here:

MSGBOX ( Have you installed a 1/4i pin and zeroed it to the table?, YesNo, Ready?)
if &msganswer = No then end

BEGINENTRY:
INPUT "Enter X value for origin offset:" &_x_offset
INPUT "Enter Y value for origin offset:" &_y_offset

INPUT "Enter X length of rectangle:" &_x_length
INPUT "Enter Y length of rectangle:" &_y_length

JZ,1
J2,&_x_offset,&_y_offset
MSGBOX ( Is the machine over the corner of your desired origin?, YesNo, Ready?)
if &msganswer = No then goto BEGINENTRY

J2,&_x_offset+0.125,&_y_offset+(&_y_length/2)
MZ,0.1

'Position end stop!
PAUSE
JZ,1

J2,&_x_offset+(&_x_length/5),&_y_offset+&_y_length-0.125
MZ,0.1

'Position edge stop!
PAUSE
JZ,1

J2,&_x_offset+4*(&_x_length/5),&_y_offset+&_y_length-0.125
MZ,0.1

'Position edge stop!
PAUSE
JZ,1

JH
END

It simply moves the router to the appropriate location on the table such that you can but a stop up to it and clamp it in place. You then slide your board up against the stops and, in our case, turn on the vacuum.

[dlcw]

Here is what I use. Been in for about 4 years now and still as tight fitting today as the day I built it all. I use 1/2" dowels in the blocks.

[Chazz]

It seems that I may have done poorly in articulating my problem. An example drawing shows how I typically use the alignment pins on a project. The parts marked in red are the holddowns that I have removed the base board bolts and run longer bolts through the material, base board and to the nut in the track in the aluminum. This seems to hold down the material just fine. Everything works fine -- until I flip them to the other side. Then, things seem to shift a little. Never much; but enough to be of concern on my jobs. I have been thinking of replacing the wooden dowels with small segments of steel rod.

Does this make sense?

Thanks again,
Chazz

[bobmoore]

You will find that you need to use 4 pins to consistently locate a flip chazz. We always used .25 router bit shanks that were broken or worn cutting edge. "Don't use steel if you leave you machine unattended at all because if you mistakenly run the wrong program, sparks will fly". The holes will wear in the spoilboard after a few flips. When this happens get some fast set epoxy to fill the holes and redrill them with your program. Bob

[cnc_works]

I use the shanks from 1/4" router bits left from trying to trim c-clamps or drywall scews.http://www.talkshopbot.com/forum/images/icons/icon12.gif

[Chazz]

Thanks folks. I imagine that the difference in the using of the broken bits vs bits of steel rod is fairly moot. I only have one broken 1/4" bit at this point. Of course, if I use steel pins, I should expect more in my future... lol

Thanks again.

[Burkhardt]

I use aluminum rod 1/2 or 1/4 inch from the hardware store. The diameter of wood dowels is all over the place.

As for drilling I found that the usual jobber bits drill a few thousand larger than their diameter. If I use an upspiral end mill in peck drill mode the hole is much more precise, actually even a tiny bit undersize. Maybe the spindle drills too fast for a jobber bit.

[knight_toolworks]

fluted downs work well they are a snug fit and they are pre cut but they are usually too long but they are cheap.