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Dowel Set-up

1/23/17       
Stewart Member

Hi Everyone,

I have searched this forum but can't seem to find what I am looking for. We are finally introducing doweling to our shop floor and are wanting to use a standard 8 x 30 mm dowel (not pre-glued). Our standard material is 19mm thick. How much of the dowel into the end bore and how much into the face? Is it better to plan on leaving a 1 or 2 mm clearance at each end of the dowel? (Or does it matter so long as there is some clearance?) Is there a standard for number of dowels in a 24" deep base and 12" deep upper? I'm thinking we have to be on 64mm centers to keep within AWI spec (?) We are planning to start the first dowel at 32mm from the face. Thanks for the help!

1/23/17       #2: Dowel Set-up ...
Bill

Based in my experience you need a 2mm gap at the bottom of the hole for the excess glue to pool. Then you need to put enough glue in the hole for it to be pushed up the sides of the dowel.

The problem is that an average assembler manually applying the glue will use less than needed so there is no squeeze out.

The answer is to get a glue application device that will apply a repeatable specific amount of glue. We use a Jolly Colla. Expensive but worth it.

You mentioned not using pre glued dowels. They work very well and are easier to have success with than glued dowels for the reasons mentioned above. You can shoot water in a hole easier and cheaper than glue.

If you are going to use a boring/insert machine water is better than glue in my opinion. If the machine stops shooting glue or water there it is not easy to tell. I suspect if you shoot glue over time you will get clogs. Then things will fail later down the line.

In the beginning we used a lamello glue bottle to apply glue. It worked well, put glue on the sides of the hole and lasted for a couple years.

I can not help you with the other questions. We overdue it.

Good luck.

1/23/17       #3: Dowel Set-up ...
Zack

When measuring for dowel outstanding the basic rule I go by is to leave at the very least 3mm of material at the bottom of your hole when you bore for your face hole. This includes the 1mm reservoir for glue. So we are talking about 12-14mm dowel outstanding for 19mm thick material. Any more then that and you will blow out the back when assembling your material.

As for pre-glued dowels they are definitely not as strong when assembling (you usually have to use PVA in the face hole anyway which means you're buying glue so why not use it for the whole dowel) and they are very temperamental to humidity and heat. *see info sheet*

As for dowel placement go with AWI standards and adjust as you see fit when in production. It will always depend on the material and application of the pieces you are making.


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1/23/17       #4: Dowel Set-up ...
Bill

Zack my experience tells me pre glue is sufficient. Steel dowels are stronger than wood but it turns out wood is strong enough.

The document you sited is a Gannomat marketing document not a technical document. Also glue coated dowels have been around quite a while.

If you are hand applying dowels by all means use glue. If you are using a bore insert machine I don't think it is worth it.

Either way will achieve success.

1/23/17       #5: Dowel Set-up ...
Larry

When we got our bore & insert we tested both systems. The glued dowels held better, BUT are they necessary? There aren't any problems maintaining the glue system, as long as you do it every time you use it, takes less than 5 minutes. At the clamp we use a Lamello pressure tank and gun. Again not a problem if you maintain the system correctly. At the drawer clamp we are using a Lamello bottle. Needs to be kept very clean. As for hole depth a little space is required just because there are always some variables.

1/24/17       #6: Dowel Set-up ...
Zack

Bill, I agree that wood dowels are all you need over steel. All you are looking for is shear strength in that respect and the material will break way before a wood dowel snaps.

I went to the Gannomat website to see if this was a marketing tool and it doesn't look like they are selling dowels so I believe that this is not so much a marketing tool as good information to inform the market. Many of their points look like common sense to me, especially the point about the glue on the dowel outstanding being activated thus making you have to use glue in the face hole. One of the aspects of a dowel is to soak up moister and expand in the hole to make a stronger joint which means the glue is naturally going to activate on the dowel outstanding when injected. It looks like any machine can shoot either type of dowel so why put out information in this respect against pre-glued dowels?

I have heard stories of pre-glued dowel construction being weak and coming apart and dowels jamming in the feed tubes because the already activated glue rubs onto the side of the tube making the dowels stick in more humid weather. I've also heard of groups of dowels sticking together because the dowels glue gets activated by the humid air. Another thing is that you have to shoot and excess amount of water into the hole to activate the glue properly which can run out onto your machine and rust parts.

I have never heard of these problems with normal dowels and glue. If you have a machine that can handle the glue properly and have employees that maintain the machine then a dowel with glue I believe makes for a stronger hold and better joint with less failure.

I would much rather have a 0% chance of joint failure due to dowel and a glue being properly installed then a higher % of failure using a pre-glued dowel installed properly. Are pre-glued sufficient? Most of the time yes, sometimes no. Depends on how you look at it

That's just my opinion though.

1/24/17       #7: Dowel Set-up ...
Bill

Zack the marketing is "our machine can shoot glue theirs can't". If it is on their website it is marketing.

I look at things in the long view. Over time what will I have the most success with and the least opportunity for things to go wrong.

All your points about dowels sticking together, the tube getting sticky I have not found to be a problem. The point about activating the glue on the rest of the dowel I also find to be untrue. The water is very precisely injected it is not running out the hole. It is shot at an angle so it bounces off the bottom of the hole and spreads to the sides and top. Unfortunately due to other problems we take things apart. When we do this we are in effect testing the holding force, it is adequate in my opinion.

My fear with injecting glue is that over time (think years) the system will get junked up (that's a very precise technical term). Everything we have glue in over time gets "junked up". I do not see why the boring machine would be different. Then at some point it will not shoot glue or not shoot enough glue and you will be putting product out the door that is held together by friction and it will fail 100%. If this happens it may be many many products that fail before you realize.

In my view it is just a matter of time before this happens and it is likely to happen more than once. We are very particular about our preventive maintenance. I have a full time person. I still believe that a pre-glued dowel over time is going to give me the most chance for success and protect me from mass failures.

Is it as strong as a properly glued dowel, probably not. Is it strong enough, I believe so.

We do glue the face side because it is easier to control glue than water in a hand applied application.

This is all my opinion based on experience. We have gone through 2 boring machines and so many dowels I would have to think about it to put a number on it. Certainly in the millions.

Can glue be used successfully, certainly. I would follow a strict testing and cleaning protocol.

Bill

1/24/17       #8: Dowel Set-up ...
Dave L

64 on center is for drawers. I thought doweled cases were 128, but that is for confirmats. Dowels are a more flexible 4 per foot.

I don't know the rule of thumb, but boring machines typically drill the edge holes ~11mm deeper. I prefer a minimum of 12mm face holes and 35mm dowels.


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1/25/17       #9: Dowel Set-up ...
Larry

"My fear with injecting glue is that over time (think years) the system will get junked up (that's a very precise technical term). Everything we have glue in over time gets "junked up". I do not see why the boring machine would be different. Then at some point it will not shoot glue or not shoot enough glue and you will be putting product out the door that is held together by friction and it will fail 100%. If this happens it may be many many products that fail before you realize."

There is a simple solution: PREVENTIVE MAINTENANCE. In our shop the boring machine gets its glue injection tested at every startup. It's simple, takes a couple of minutes, cheap insurance. At shut down the machine nozzle is cleaned, wiped with a light coat of oil and ready for the next day. Once a year the systems on all machines are taken apart: cleaned, lubed, checked for wear, etc. PM! This is addition to the day to day maintenance. In all the years we've run this way we've never had a call back for a joint failure.

"Unfortunately due to other problems we take things apart." Know it too well, but if you call it quality testing it sounds better.

1/26/17       #10: Dowel Set-up ...
Bill

Larry I am glad you chimed in. I believe I have read this before from you. It is part of my thinking on this subject and good insight for someone who wants to use glue.

Although we have a strong PM program the daily upkeep is not what it should be and I would be uncomfortable adopting this strategy. Lessor of the evils so to speak.

Thanks

1/26/17       #11: Dowel Set-up ...
Larry

Bill, I can understand that.
If you allow more than one user of a machine, you have to have one of them take ownership and make sure "their" machine is taken care of. I'd like to say this is 100% affective but it only works with certain people.

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