Need advice on mastering locator pegs/holes

[Alfred Wong]

This is something I've never gotten the hang of; making locator holes and pegs on mating parts. I currently try to attach a peg on 1 part then try to measure in the hole on the other part, then try to drill the hole. But if the drill wanders even a millimeter the alignment is spoiled. Then it's even more difficult or impossible to make a new hole. I'm also a really crappy driller. So, does any of you other master-makers out there have any fool-proof techniques to share?

Thanks in advance.

[Mark Yungblut]

While I worked at the model shop, we would often have to make precision locator pegs. We always resorted to building a jig that would allow us to hold the plain iof the surface to be mated level (for both pieces). Quite often, I would tack the pieces together with a bit of super glue and mark a line at the point where the pin needs to be located (lets say the area where a wing meets the root). general rule of thumb is to let the thinner piece or smaller piece detirmine where the pin sits from a cross section standpoint. I would measre from at least three directions and mark the hole. I would then place the the part in the jig and check to make sure the plain where the parts meet is level. Using a drill press or Milling machine (if you are that lucky) drill a pilot hole. This will help to ensure that there is no wabble while drilling the hole to the final OD of the pin. This can be repeated for each part and pin.

Hope this helps.

[Alfred Wong]

And if one doesn't have a drill press or a milling machine? I just have a pen-vice.

[Andrew Gorman]

I am getting better at pinning joints, and have learned two things:
1. Make a "doweling pin" - Drill the hole on one part, and make a short, pointed pin that just breaks the surface. Line the parts up where you want them, check everything, take another look and check it again. If it looks good, press the parts together to make a little mark where the pin protrudes. I use dollar store safety pins that fit nicely into a # 65 hole and are easy to cut to lenght with a par of nippers. This will mark fairly exactly where you need to drill the hole on the mating part.
2. Make a good center! You'll need to make your light mark from step one a little larger to get a good start with the drill. Chuck a needle (or another chunk of safety pin) into the pin vise, and poke it into the light mark you just made. Make it a little deeper and check it again with the pin in the other part. This is your best chance to make a correction. If the location is off, use the chucked needle to make another hole and try to obliterate the original by wiggling the pin. You want a perfectly located and straight pit to start yhr drill.
With a good center mark, start drilling. Do it by hand with the pin vise, and really work at going in straight. If you start off with a much smaller drill thean the hole you finally want, you have a little more chance to make corrections as you increase the drill size.
It really isn't hard to do, just measure twice, cut once. And it's very satisfying when tow parts just snick right into place! There's a good article on this from a woodworker's perspective at:
http://www.americanfurnituredsgn.com/Pe ... Joints.htm
And a search for "machinists + "use of the center punch" could turn up some good information. Hope this helps,
Andrew

[Kylwell]

I would also like to add that drilling slowly with a sharp bit really helps. I've gotten to the point where I can drill out tiny little barrels when needed. I also found that the cordless dremel really helps.

I've never tried to pin a part but here's my initial thought as to how I'd give it a whirl.

Drill hole(s) into part A
Cover part A with cling flim.
Drop pin(s) into hole(s) through wrap.
Drill largish hole(s) into part B, much large than pin(s)
Smear epxoy into hole(s) in part B
Press parts A & B together until epoxy hardens then pull apart. Hopefully the cling film will minimise the epxoy glung the to parts together.

Now, if you're doing multiple holes & pins you;re going to need to get them as perpendicular to the mating surface as possible, but, you could always hog out the hole a bit to make up the difference.

Now that I've stated that, I'm going to have to give it a try.

[DennisH]

I don't know how feasable it would be for what you're working on, but you can clamp/join the two halve together temporarily.

Drill one hole through both pieces or through one and into the other. Then using a "pin" the same diameter as the bit, plug the mail hole with it, leaving some sticking out for your pin.

Finish off the surface(s) you drilled through so it doesn't show and you're golden.


Dennis

[Kylwell]

Oh fine, come up with a simple method why don'tcha...

[Alfred Wong]

Dennis' method would only work on a limited number of instances, where the parts have at least 1 relatively thin piece and where ruining the surface detils is not an issue.

[TER-OR]

I usually use the method kylwell described. Packing tape works well, too.

When pinning parts together I use the method Andrew described. Make sure you have enough pin to grip with a needle-nose pliers, or you'll find yourself stuck.

Another option is to use strips of plastic, not pins. L-shaped or even just linear strips.

[Quantum]

I use AG's method, but use lipstick, in home improvement projects; specifically, drilling out the hole in a door jamb for the strike plate. It should transfer to what you're trying to do: put a little on the pin side, press the pieces together, and there you go.

[Blappy]

And if one doesn't have a drill press or a milling machine? I just have a pen-vice.

Spend $85.00 Canadian and get one. For what you do its indespensible. You can put a sanding drum in it and all kinds of wonderful things that speed up the construction process.

http://busybeetools.ca/cgi-bin/picture? ... ITEM=CT024

[Blappy]

Dennis' method would only work on a limited number of instances, where the parts have at least 1 relatively thin piece and where ruining the surface detils is not an issue.

For Dennis' method you could do the drilling before you add the external details.

[DennisH]

Blappy wrote:

For Dennis' method you could do the drilling before you add the external details.

Hey!, I was going to say that.

That technique really depends on the situation. Knowing that Alfred fabricates a lot of patterns (I'm assuming he is talking about being in the prototype phase), he could do that in the early stages of construction before it became an inconvenient process.

Now, if it's an exsisting injection molded kit for instance, that would make it more difficult not to fudge up the details.

Another way, would be to get small diameter pipe or tube, say 1/8"O.D. with a 1/16" hole. Pin one length with 1/16" brass rod and attach it to the inside of one of the pattern halves. When that is secure enough, drill out the other piece of 1/8" slightly so the pin can slide in and out easily, but not too easily. Then slip it on the pin, add a little adhesive (glue, solvent, epoxy) to the unsecured piece where you need it to attach to the other half of the pattern and align the two halves until the adhesive sets. Pull the halves apart and then secure the second piece more stringently. Make it all nice a pretty-like and your ready to mold it. Once it's cast solid, it will be just like any mass produced item with stand-off locators(sp?)

Does any of that make sense? I've done this before, but with the constraints of client deadlines, I've never taken pictures of what I'm talking about or I'd show you. Take apart anything held together with screws and look at how it is made (radio, kids toys, remote controls). you should see what I'm describing.

I'll be quiet now .


Dennis

[Alfred Wong]

Yes Dennis, that makes sense, it's a pretty good idea! Thanks.

[Blappy]

Blappy wrote:

For Dennis' method you could do the drilling before you add the external details.

Another way, would be to get small diameter pipe or tube, say 1/8"O.D. with a 1/16" hole. Pin one length with 1/16" brass rod and attach it to the inside of one of the pattern halves. When that is secure enough, drill out the other piece of 1/8" slightly so the pin can slide in and out easily, but not too easily. Then slip it on the pin, add a little adhesive (glue, solvent, epoxy) to the unsecured piece where you need it to attach to the other half of the pattern and align the two halves until the adhesive sets. Pull the halves apart and then secure the second piece more stringently. Make it all nice a pretty-like and your ready to mold it. Once it's cast solid, it will be just like any mass produced item with stand-off locators(sp?)

Does any of that make sense? I've done this before, but with the constraints of client deadlines, I've never taken pictures of what I'm talking about or I'd show you. Take apart anything held together with screws and look at how it is made (radio, kids toys, remote controls). you should see what I'm describing.

I'll be quiet now .


Dennis

I have seen this method done on a figure kit. The person used square brass tubing of two different sizes that telescoped together. It was VERY efective and insured the parts would line up exactly and in the correct orientation.

[DennisH]

WHEW!!!! O.K. then! I was worried that I sounded like a lunatic.


Dennis

[karim]

Another version of Dennis' method is to drill the clean alignment hole FIRST. Call this hole "A"

Cut the rod that you want to form the "pin" to go in hole "A" about twice the depth of hole "A".

Now the SECOND hole ("B") you drill is going to actually be be the permanant home of the locator pin, so you can drill it larger than it needs to be to give you some wiggle room.

Rough up the surface of the pin that extends out of hole "A" and the inside surface of hole "B" and put a little epoxy putty in hole "B".

Dust the mating surfaces (not the Pin or hole "B"!) with talc or cornstartch, and then push them together, settling the roughed end of the pin into hole "B".

When the epoxy putty cures, you should be able to pull the pin, now attached to the hole "B" side out of hole "A", and the parts will forevermore align on that pin.

Now just clean up the joint between the pin and hole "B" (there are bound to be some gaps).

[Alfred Wong]

That's good too! I like those ideas. Blappy, while I know that a drill press can be handy, (I do have access to one next door, and I often use it) it's not always practical for the odd shaped things that are the norm. Often I found that trying to jig them for a drill press is waaay more hazzle and problematic than anything else.

[Kylwell]

That's good too! I like those ideas. Blappy, while I know that a drill press can be handy, (I do have access to one next door, and I often use it) it's not always practical for the odd shaped things that are the norm. Often I found that trying to jig them for a drill press is waaay more hazzle and problematic than anything else.

I've found using the yellow poster stick-em stuff works great for bracing small odd shaped items for drilling. It just takes longer working from little tiny drill to the size needed. Once SueChef gets her Casteline I may experiment with it for bracing parts.

[Mark Yungblut]

Alfred,

The technique i wrote about is what we did to get "super accurate alignment. I would go with the telescoping tbing idea. Drii the hole free hand and put the tubing in with epoxy putty. Should work great for those odd shapes.

[Woody]

I love my Microlux variable speed drill press.
http://img.photobucket.com/albums/v140/ ... 334590.jpg
http://img.photobucket.com/albums/v140/ ... 4107ae.jpg

I like to use templates for aligning pin placement between two parts. Trace the end of one of the parts your trying to create pins for onto a thin sheet of styrene. Take a straight edge and draw a line through the center of this template. Draw a perpendicular line at the points were you would like to have a pin and it's locating hole. Cut out the template on the line you traced off the parts end. Drill small holes in the template at the intersection of the lines you drew. Place the template back on the first part and using the same small drill bit drill a hole in the part using the templates holes as a drilling guide. Flip the template over and position it on the mating surface of the other part. Using the same small drill bit drill the holes again into this part. Switch to a drill bit size that matches your pin size. Using the first set of holes as pilot holes, drill both parts to the depth you need for the locating pins. Cut your pin stock slightly shorter than twice the depth of your locating pin hole. Glue the pin into which ever part will have the locating pins. You may have to dress the pins a bit with sandpaper so they aren't too snug.
A quick note for easy and neat pin gluing. Use styrene tube stock with one end caped by styrene sheet, sanded flush to the tube stock. Place a drop of thin CA into this pin. With the open end facing upward, slide it into the hole you have drilled to accept it. Tip it up and the glue will run down leaving you with a perfect bond and no clean up.

[Padawan v 2.5]

Not to be impertinent, but when I'm building a model, the first thing I do is nip off all the alignment pins as they are seldom straight and often interfere with assembly. If you're mastering models to be cast in resin, maybe it's best just not to worry about the pins at all. Most modelers who work in resin have been around the block a time or two and can handle a model without them. Just a thought.

K

[TER-OR]

Unless, of course, wing alignment is important - or something along those lines. Then a pair of good holes and a bit of metal rod which can span the parts makes life MUCH easier. That can be done by the telescoping method, used again in reverse on the original side.

[Vince Hoffmann]

I don't pin anything, I just use lots and lots of glue!

[Joseph C. Brown]

I don't pin anything, I just use lots and lots of glue!

Hey! That's what I was going to say!