# Fasteners : Screws Vs Taper Pins Vs Dowels



## BillWood (Jul 19, 2015)

Hello,

Following issues raised in another thread am wondering what books websites etc I have to read to better understand when to use screws vs taper pins vs dowels for holding things together ?

And what place do modern adhesives have in metalworking - ie I am aware of various strengths of loctite and am also aware of 2 part epoxy.

Haven't seen much discussion of these things in my various books.

I guess most of my books are about using the tools to cut things up  rather than sticking things together - is there a good basic fabrication or sticking things together book ?

Bill


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## JimDawson (Jul 19, 2015)

Great questions!

As an old tool&die maker building maintaining stamping dies, I have been working with dowel pins for many years.

So when should dowel pins be used?

Dowel pins are used in conjunction with the bolts to maintain precise alignment of the parts of the tooling.  There is always some lateral movement possible with bolts, if they fit tight in the bore, you couldn't get the bolt in.  Dowel pins also allow you to remove the tooling from the base (die set) for sharpening and repairs and be able to put the tooling back exactly where it was without having to go through the initial build alignment procedure all over again.  When dies are built, the tooling is bolted into place, then aligned properly, then as about the last operation, the dowel pin holes are drilled and reamed for a tight fit.  The dowel pins prevent any lateral movement, while the bolts secure the tooling to the die set.  Dowel pins are normally installed with a tight fit, requiring a hammer & punch or a press to install and remove.  Normally installed in through drilled holes so they can be punched through to remove.

So bottom line, if you don't want any lateral movement in any assembly, use dowel pins to prevent that.

Taper pins do exactly the same thing as dowel pins, maybe with even better alignment than dowel pins.  But are harder to install properly because of the taper and require the use of tapered reamers.  Taper pins are good for installation in a blind hole, and are many times threaded internally so you can extract them with a puller.  You normally find taper pins aligning parts of machine tools, especially the older iron.

A lot of the modern equipment uses spring pins for alignment when ''precise'' alignment needs to be maintained.   Much easier to install, just drill a hole and pound the pin into place.  Reduces manufacturing costs, but not as good as dowel or taper pins.

Sticky Stuff

We all pretty much know the uses and grades of LockTite and similar products.  If you don't want that bolt to come loose, use red LockTite, and it's pretty much there for ever.  Red is also used for securing SpeedySleaves to shafts.  SpeedySleaves are used to repair worn seal surfaces on shafts, including main seal surfaces on automotive crankshafts.  The blue stuff doesn't set quite as hard, and disassembly is easier.  LockTite also has a bearing mount product that is said to fix some problems with bearing bores and shafts that have had a bearing spun on them and caused wear, I think the limit is about 0.010 wear.  I have never used the stuff.

I glanced at an article the other day about gluing car frames together, I haven't read through it yet.  I guess it's in the experimental stages.

I am also a real fan of 3M VHB tape products, this stuff is great for sticking stuff together.  It's pretty good in shear and tension, but not so good in peel.  Good chemical resistance for most petroleum products, and water based solvents.  It doesn't like MEK, acetone, and other stuff like that.  I believe Grumman Aircraft was using the VHB products to attach the skins on their non-pressurized aircraft.

The most common metalized epoxy available for normal shop use is JB Weld.  It can be used in a lot of places for lightly stressed metal repairs.  It's machinable, drills & taps with reasonable holding power.  With proper preparation, will seal up a cracked engine block in many instances.  Could be used to repair a broken casting, but again only a lightly stressed part.  I've never found anything metal that it won't stick to.  It can also be used with some plastics with varying degrees of success.

.
.


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## plus1hdcp (Jul 19, 2015)

As a new person here, thank you Jim for this informative response.


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## T Bredehoft (Jul 19, 2015)

JimDawson said:


> LockTite also has a bearing mount product that is said to fix some problems with bearing bores and shafts that have had a bearing spun on them and caused wear, I think the limit is about 0.010 wear.



That reminds me; I once was asked to measure the cavity in which had been a bearing that had destroyed itself. The outer shell had been removed, the shaft had been removed. I was in a cavity something over 4 feet in diameter. (The shaft was vertical) There were scraps of olive green plastic about .010 thick all over the floor, Maintenance said it was LockTite that had been around the old bearing. I strung together a bunch of pieces of ID mikes and measured the hole in half a dozen places, coming up with a figure for the OD of the bearing. The machine went back in service, no one told me I had screwed up the measurement, so I guess I got it right.


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## John Hasler (Jul 19, 2015)

The Loctite product used for bearings is 660.  I've used it in tractors.  It's very effective.


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## royesses (Jul 19, 2015)

I used to install Jiffy sleeves on crankshafts when I worked for CAT. I used CATs version of shaft and bearing mount along with surface primer to get a liquid tight spin free sleeve installation. A quick pass with a torch was need to remove. Saved the customer thousands of dollars in repair costs. I also used shaft and bearing mount when machining blocks and  installing cylinder block inserts to bring the deck up to spec.  Also used hollow dowels to repair front cover oil leaks at the air compressor oil feed where the gasket was leaking. Drill and ream the front cover and adapter plate and press in the dowel with bearing mount on the cover side only. This saved about 17 to 20 hours of labor.


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## RVJimD (Jul 20, 2015)

Excellent question and really nice information from Jim!

Thanks,

Jim


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## tertiaryjim (Jul 20, 2015)

Nice explanation Jim. Thanks!
As I've seen so many machines messed up by those misusing dowels ,loctite, and RTV ,this thread seems a good opportunity to address a personal peeve.
Taper dowels are Not driven into their holes. The machine components must be aligned and the dowels slipped in. Taper dowels are usually soft so they are destroyed before damaging
the precision holes they go into. By driving them in the taper dowel and it's mating hole is distorted- loosing proper alingment.
Have seen machines glued together by poor use of loctite and rtv. Select the proper grade and use the minimum amount.
In the case of RTV, it usually requires a small bead ( very small ) in the seal area only. Not the entire joint.
Then there's antisize. The components must be clean and the antisize must be brushed into the threads to cote and  work properly.
Have seen plenty of guys that would dip a bolt into the can and install bolts dripping with antisize. Now antisize would get spread everywhere except deep in the thread where it's needed.
Even the most simple of components must be used properly.


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## Bill C. (Jul 20, 2015)

I remember when working as a lab technician for a local university the professors used Eastman 910 to secure strain gages to steel and plastic. Superglue of its day.

Great article Jim


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## John Hasler (Jul 20, 2015)

Bill C. said:


> I remember when working as a lab technician for a local university the professors used Eastman 910 to secure strain gages to steel and plastic. Superglue of its day.
> 
> Great article Jim


The 910 formulation is still available from Permabond.  Superglue is a pale imitation of it.


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## Bill C. (Jul 20, 2015)

John Hasler said:


> The 910 formulation is still available from Permabond.  Superglue is a pale imitation of it.



Thanks, I didn't know 910 was still available. I had one professor glue his finger tips together with it. He ended up in the ER to have his fingers cut apart. 

And yes Superglue can't compare to 910 and other quality glues.


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## Bill C. (Jul 20, 2015)

If you use pull pins be sure to use either the ones what have a spiral groove cut in them or grind a small flat along the length of the pin to break the seal.  I had a few installed in a die section and I turned around to find one had popped up about 1/4" above the surface.


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## John Hasler (Jul 20, 2015)

Bill C. said:


> Thanks, I didn't know 910 was still available. I had one professor glue his finger tips together with it. He ended up in the ER to have his fingers cut apart.
> 
> And yes Superglue can't not compare to 910 and other quality glues.


Acetone will (slowly) soften cyanoacrylate.


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## BillWood (Jul 21, 2015)

Many thanks for the responses.

Will do some practicing on my next project with taper pins, dowels and screws.

Bill


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## Tozguy (Jul 22, 2015)

No more about glue, now I'm stuck!


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## Richard White (richardsrelics) (Apr 18, 2016)

I also am a Tool and Diemaker, straight dowels are as he stated, for precise die work to ensure absolutely NO lateral movement.  On the personal side, I see taper pins in outboard power head crankcase halves, and they must be slid together for alignment,so you have the taper to allow it to slide together so when the 2 halves meet the pin gives final proper alignment. I would guess they, the taper pins, are probably used alot on case halves.


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## ChipsAlloy! (Apr 19, 2016)

We often see taper pins used to lock taper bushings, gears and cams on their shafts in the packaging industry. We use taper pins to prevent reversed installation of critical components that must be synchronized. It helps make things somewhat fool proof because you cant just insert the pin its full lenght if the tapered holes are reversed.


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## Wreck™Wreck (Apr 22, 2016)

JimDawson said:


> Great questions!
> 
> I glanced at an article the other day about gluing car frames together, I haven't read through it yet.  I guess it's in the experimental stages.



I had a Suzuki motorcycle that had a rear wheel swing arm that was made in three parts, an aluminum casting and two aluminum weldments glued and screwed together and seemed to work well, it was manufactured in 1991.

Several years ago I made  pipe flange molds that would form the grooves on the sealing surface of damaged flanges used in steam applications, in place.
The epoxy was placed on the damaged face then the mold, with a release agent was bolted to it thus forming the ASTM designated grooved surface required.
Also made molds for repairing damaged bearing journal surfaces on shafts for the same Company, they claimed that 1 of their epoxy products for this application was un-machinable with single point tools and should only be ground.

I have no affiliation with this Company and haven't done any work for them in several years, if one wants to look into some advanced epoxy products they are called Belzona, an Italian Company


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