Help...using DOWEL PINS

[mecheng2006]

Hi,

Looking for some help here, i'm looking into using a dowel pin between two zinc cast parts...

i've never seen a hinge design use dowel pins before and I was wondering if there was any particular reason for that?
Does anyone know if it would be an issue. The door for this apparatus will be used very often. Is there anything that I should be paying more close attention to???

thanks for all your help!

Mecheng2006

 

[tygerdawg]

use dowels for a hinge pin? Methinks you will discover the dowels have much higher hardness & cost than a normal pin.

TygerDawg

 

[mecheng2006]

hi tygerdawg,

i`ve verified the cost for using a hinge pin and it looks like using dowel pins would bring in a cost savings for me. i did notice that the dowel pins would have a higher strength as compared to the hinge pins but i`m not sure if a dowel pin should be used for this type of application?
These dowel pins would be press fit into the Zinc castings, i`m not sure if this would bring about issues in terms of fatigue?

any help would be greatly appreciated!

mecheng2006

 

[FACS]

Maybe it's the press fit that denotes a dowel, as they have tight tolerances. Also, they are probably stainless dowels??? If so, then perhaps there is a corrosion issue.

It's good you look for reasons instead of just changing for the sake of change.

Charlie

http://www.facsco.com

 

[mecheng2006]

well, the dowel pin that I am looking to use is made of hardened steel with a zinc coating for corrosion resistance. my main concern would be potential issues in the door sagging during repeated cycling as the dowel pins will be press fit into the hinges.
is anyone aware of someone using dowel pins in a pivot joint? I have only really used them for positioning and alignment for mating parts....

any advice would help!!!

thanks

 

[bonbon123]

Dowel pins are much more precise in dimensions as well having very close tolerances. For door applicaton, a rod (cut to size) would normally do the job for less cost than dowel pins (in qty). There are lots of plastic (delrin) pre-fabricated hinges that are available too, but of course you also need to consider the weight of the door. Life cycle of these hinges are very reasonable if the parameters are within it's designed specifications.

 

[John2004]

You can get drill rod from

http://www.mcmster.com.

It's not held to as close of an OD tolerance as a dowel pin, but their made of tough tool steel and pretty close OD tolerance. If you buy them in length and cut them down, it may be cheaper than a dowel.

Can you put some low cost plastic bushings from

http://www.igus.com

in the hinge? They are self lubricating, quiet, take very high loads, and should last forever on a door hinge if the environment is half way decent.

As far as using dowels in a pivot situation, I have heard of them used as bushing shafts, and they wear about like standard bearing shafting.

If it's cost effective for you then it sounds like a dowel should work, but a hardened dowel kind of sounds like overkill for a door hinge unless it's a really heavy or high stressed door.

Good Luck
John

 

[mecheng2006]

My current setup uses a hinge pin made of hardened tool steel where we are using bronze bushings which are press-fit into a zinc casting(serves as a hinge). the other zinc casting is connected via the hinge pin and is bolted down.

i'm looking into removing the bushings and the hinge pin and replacing it with 2 dowel pin on both ends. Cost analysis shows that the dowel pin is a cheaper alternative but my main concern would be the slop between the two hinges after several cycles. i would tend to think that the door would begin to sag because of the wear in the zinc casting... i'm not sure at this point.

does anyone have any additional advice?

thanks!!!

 

[John2004]

Hi Mecheng2006,

Is the reason for the design change a need for lower cost or do you currently have a wear problem at the bushings ?

If you are concerned about wear, why are you removing the bronze bushings ?

The plastic bushings from

http://www.igus.com

may wear much better than the bronze bushings and are probably cheaper. If you go to the Igus site, they have an online life estimator called their "expert system" that will give you life estimates for just about any given application scenario. They also give the program out on CD-ROM. These bushings are better than bronze in many applications, especially oscillating non-lubricated applications.

Another option are self lubricating metal bushings from

http://www.peerinc.com

The Peer bushings also have very low wear, have very high PV values and are cost effective. They don't tolerate misalignment as well as the Igus bushings, but that may not matter to you.

Why not use the dowel pins, but replace the bronze bushings with a self lubricating bushing that wears well in oscillating applications, like the Igus or Peer bushings ? I would check into the Igus bushings first.

If you could provide a little more feedback as to exactly why you want to make the design change, you may get some more meaningful advice.

Hope this may have helped.

John

 

[MikeHalloran]

Dowels require very tightly controlled holes, which are expensive to produce, especially in smaller sizes. Even so, the interference produced is not great. If the dowel is not driven deep (and a deep small dowel hole is still more expensive, it may be possible to work it loose with your bare hands.

It's more common to see roll pins used as hinge pins and pressed into zinc, because there's more interference, the hole tolerances are looser, and the pins are easier to drive fast.



Mike Halloran
Pembroke Pines, FL, USA

 

[Speedy]

A little shop secret I was told by a toolmaker once;

If the dowel hole is too big, that the dowle is too loose. Place a ball bearign ball over the hole and belt with a hammer. How hard you need to hit it and what size ball, i'll leave to you.

Be careful, as teh ball will fly!

Speedy

 

[mecheng2006]

Hi all,

I am looking at removing the bronze bushings and the hinge pin altogether because of a cost reduction idea. also, with our current setup, the hinge pin is running through two zinc die cast parts. because of alignment issues, we found that there were some hinges which were more difficult to engage because of the increased friction between all the parts...

John, I already looked at replacing the bushings with a plastic bushing through IGUS but, it turns out that the cost is almost double that of our existing bronze bushing.

mike you bring out a good point in terms of the tight hole tolerances needed for dowel pins, i'm going to look into the process capability from our supplier in terms of getting the kind of hole tolerances for a press fit function in zinc castings... but my main concern at this point, is the use of dowel pins as a hinge connection and the removal of the bronze bushings. I believe that over time, the holes will enlarge and my door will begin to sag. i'm not sure what kind of mech properties zinc castings have in this application but i'm looking for advice...

thank you all!

 

[John2004]

Hi Mecheng2006,

If the Igus and Peer bushings are too expensive, and you cannot find another bushing that wears well and is cheap enough, you might want to look into making the hinge material itself out of a bearing material (if the zinc won't do the job).

There is a tool steel(I think 0-6) that has self lubricating graphite properties. You may want to check into something along these lines. I don't know what type of environment you have, i.e., how much rust resistance you need etc.. Also, your casting supplier may be able to add something to the casting to provide self lubricating properties, or recommend the best wearing material.

The problem with using the casting as your bearing surface is that when maximum wear occurs, you have to replace an expensive casting instead of a cheap bushing.

http://www.mscdirect.com

has some "DU" split type self lubricating metal bushings that are cheap, you might want to search their site for size and pricing information. These bushings are made by

http://www.buntingbearings.com/

and they make many other bushings as well. You may want to contact them for bushing advice.

You may have to set up a test rig in order to find out if the zinc will wear well enough for you. Many times bushing engineers will tell you testing is the only real way to determine how much material will wear off a bushing ID for a given application and time period. Slow moving oscillating applications can be harder on bushings than higher speed full rotating applications.

Can you make the hinge out of hardened tool steel and then put grease on it ? This might be more expensive than bushings, I don't know.

Can you put a grease fitting on the hinges and lube them periodically, or does it have to be more clean and maintenance free ? If you can specify the correct lube interval, you might get acceptable wear without bushings.

You might also try

http://www.thomasnet.com

and see if someone makes a stock hinge that will do what you need.

Can something be done to the door to take the load off and/or prevent sagging even if the hinge does wear ? Can the door be made from a more light weight material ?

That's about all I can think of at the moment, but I suspect in order to really find out what you are asking, you will have to build a test rig that opens and closes the door at a specified rate, and then after a certain number of hours, measure the amount of wear that has occurred. The zinc will wear, but it's just a matter of whether you will get the service life you need from the door or not. It's too bad you can't just find a bushing that is cheap enough for you.

Good luck,

John

 

[unclesyd]

You might look at Drive-Lok spring pins or Lok-Dowel pins.

http://www.driv-lok.com/springpins.asp

Or you might want to look at a Groove-Pin

http://www.groovepin.com/pin-type.htm

This could enable you to use your cast parts as a bearing as posted by John2004

 

[mecheng2006]

Hey John,

Ì have a test rig setup to check whether there will be any door sagging because of the wear in my zinc castings but I would like to know if there are other potential concerns that I should keep an eye on. With the removal of the bushings, there is a big potential of wear for my casting. My supplier has suggested to change from ZA-8 to Zamak 2 but I`m still looking into this.

Also, was wondering what kind of class fit should I make between the zinc castings and my dowel pins? I would like to use a 1/4 inch dowel pin...

Any help is greatly appreciated!

Thanks,

mecheng2006

 

[DAVIDSTECKER]

One thing you might consider is since you already have enough material in the casting to drill out and install a bushing is to increase the diameter of the hinge pin to further reduce the pressure in the hole.
Another thought is to make the pin the weak link in the system. It's a lot cheaper and easier to replace down the road. Maybe make it from a bronze or even a grey iron which has fairly decent bearing properties.

 

[MikeHalloran]

Good point; other materials deserve investigation. Example: some Southco hinges have plastic pins.

Another point: We here don't know how often the doors are cycled, or how fast, or for how long, or what constitutes excessive wear or other failure conditions, so we're shooting in the dark, again. If the bronze bushings had any sort of wear problems, then zinc on steel is not going to improve the situation.



Mike Halloran
Pembroke Pines, FL, USA

 

[mecheng2006]

Hi,

We did not have any concerns with the wear of the bronze bushings but at times the hinges were difficult to engage because of the misalignment of the holes between the two zinc castings. With the use of the dowel pins, we would eliminate this concern. the doors are not cycled to often and are at a low rpm. Still not sure if zinc has enough wear properties to allow the removal of the bushings, my test rig will have to evaluate it's performance. Anyone have any idea on what kind of press fit I should have between the dowel pins and my zinc castings???

thanks!