[dneisler]

I am building me a sub-plate for my machine like what we use at work. I it will have a bunch of 3/8-16 holes and 3/8 dowel pin holes. My question is what drill and reamer size to use. At work for 1/2 we use .484 drill, and and a .5005 reamer for a nice slide fit. So using that assumption I am guessing to use a .3594(23/64) drill and a .3755 reamer. This is for a precision slide fit. I may need a small slide hammer to remove them, but not a press fit or hard to remove. My confusion comes from dowel pin reamers that are undersized for dowel pins...assuming that is for a press fit?

Just need to know so I can order the correct stuff from Enco.

[Geof]

Dowel pins are used to align two holes, and the parts they are in of course. Sometimes you want the dowel pins to stay with one part but be a sliding fit in the other. On a subplate probably the best idea is to have the sliding fit holes (i.e. 0.0005 oversize) so the pins release from this plate. On the fixtures that attach to the plate you have the interference fit (0.0005 undersize) so the dowel pins stay with this part.

[karloterrazas]

If You have a 0.250 dowel pin and you want it to be press fit, You will need a .249 reamer, if you want a soft fit then you need a .251 reamer. If you need it press fit, make a thru hole and use a hammer to fit the dowel pin,

[hanermo]

Try to use a press to fit the pin and not a hammer. A hammer can enlargen the head of the pin, and you may not want that.
A big vice, machinist clamps, or threaded rod with 2 crosspieces rather than a hammer.

[viking73]

You could go a step further and press in dowel pin bushings.

[handlewanker]

Hi, I ream for dowels with a hand reamer in the mill/drill whatever.

The hand reamer has the length tapered for a 1/4 of it's length to allow easy entry in the undersized hole for normal hand reaming.

If you ream with the two halves together and go through the top half and into the bottom half just with the taper, the dowel will be a sliding fit in the top half but a press fit in the bottom half.

BTW, rollpins ARE NOT DOWEL PINS and should not be used to allign, locate or position components that need to be an exact fit.

Roll pins can be used to fix two halves together with moderate accuracy and are hardened and flexible and roll to a smaller diam when forced into the hole which is drilled not reamed, but due to their ability to downsize when compressed will not locate as acurately as a reamed in situ dowel pin.
Ian.

[juergenwt]

A tap fit for a 3/8 dowel pin - use a drill 1/64 under size and ream with a o.3748 reamer. If you want one side to slide - depends on whether you harden your part or not and the steel it is made from. CRS 1018 will close up so ream .3755 for a sliding fit. Tool steel will stay the same or open up (O-1) - so ream .3752. Regardless - you may have to hone one side or the other after HT. Don't worry about the dowel pin expanding when hit with a hammer. Unless you use some really cheap pins there is no danger of the pin mushrooming when hit with a hammer. Never happened in 50 years as a tool and die maker.

[John J. McGuirk]

If You have a 0.250 dowel pin and you want it to be press fit, You will need a .249 reamer, if you want a soft fit then you need a .251 reamer. If you need it press fit, make a thru hole and use a hammer to fit the dowel pin,

Never use a hammer. The pin will go in, but it will not be straight. And a through hole is not always possible.

[John J. McGuirk]

You could go a step further and press in dowel pin bushings.

Back to square one, proper reaming for the bushings.

[John J. McGuirk]

Hi, I ream for dowels with a hand reamer in the mill/drill whatever.

The hand reamer has the length tapered for a 1/4 of it's length to allow easy entry in the undersized hole for normal hand reaming.

If you ream with the two halves together and go through the top half and into the bottom half just with the taper, the dowel will be a sliding fit in the top half but a press fit in the bottom half.

BTW, rollpins ARE NOT DOWEL PINS and should not be used to allign, locate or position components that need to be an exact fit.

Roll pins can be used to fix two halves together with moderate accuracy and are hardened and flexible and roll to a smaller diam when forced into the hole which is drilled not reamed, but due to their ability to downsize when compressed will not locate as acurately as a reamed in situ dowel pin.
Ian.

Handlewanker
Sheesh... I feel like I'm on a porn site.
Roll pins are fine for aligning parts that are to be machined together and need not be taken apart afterward.
Dowel pins are used to align two parts "back" together after a needed separation.
Is Geof whispering in my ear?
They are also used to make jigs and fixtures, no mating part need be involved, but if the fixture is designed for multiple use, or contour milling the pins need to be removable.

[John J. McGuirk]

A tap fit for a 3/8 dowel pin - use a drill 1/64 under size and ream with a o.3748 reamer. If you want one side to slide - depends on whether you harden your part or not and the steel it is made from. CRS 1018 will close up so ream .3755 for a sliding fit. Tool steel will stay the same or open up (O-1) - so ream .3752. Regardless - you may have to hone one side or the other after HT. Don't worry about the dowel pin expanding when hit with a hammer. Unless you use some really cheap pins there is no danger of the pin mushrooming when hit with a hammer. Never happened in 50 years as a tool and die maker.

I tend to agree with you, and who am I to argue with fifty years in tool and die? I'm only almost that good.
But today, and you may be unaware of this, dowel pins are made from material such as 303 SS, hit it with a hammer and it does mushroom.
I'm often asked to cut 3/4 length to 1/2 inch, or 1/2 inch to 3/8, or whatever, and I do so on a lathe using a carbide tipped cutoff tool.
That would not be possible if we were talking about the pins we both think of as dowel pins.
Go to Grangers and look at what they sell as precision dowel pins.

[juergenwt]

John - absolutely true. I guess that if you buy dowel pins today it pay's to read the description on the box. Just like all the metal cutting tools being advertised as : "Finest Quality High Carbon Steel". Translate to: JUNK!

[Geof]

........ Don't worry about the dowel pin expanding when hit with a hammer. Unless you use some really cheap pins there is no danger of the pin mushrooming when hit with a hammer. Never happened in 50 years as a tool and die maker.

I don't care if you have been a tool and die maker for 50, 150 or 250 years, I think hitting a dowel pin in with a hammer is sacreligeous. Tapping it gently home using a brass drift is okay.

[juergenwt]

Well Geof you have a lot to learn. Take it from an old timer. When you drive in a (good quality) dowel pin ( not a soft or a stainless or aluminum pin) by using a steel hammer you can tell by the sound and the feel of the hammer if the pin is moving or if it is freezing up. And if you ever had to remove a frozen dowel pin you will from than on listen to that hammer. Trying to remove a frozen dowel pin is something you don't ever want to do. Believe me. A brass hammer is a no-no. So is a brass or copper driver. That is why your knock-out punches are made from hardened steel.
Here is where they separate the man from the boy's - my friend. Good luck to you - Try it and listen. Juergen.

[Geof]

Well Geof you have a lot to learn. Take it from an old timer....

I rather doubt you are much, if any, oldtimer than me.

[RICHARD ZASTROW]

I'm probably older than both of you. Now, get back to work.LOL

Dick Z

[John J. McGuirk]

John - absolutely true. I guess that if you buy dowel pins today it pay's to read the description on the box. Just like all the metal cutting tools being advertised as : "Finest Quality High Carbon Steel". Translate to: JUNK!

Ahh! But junk in the finest sense of the word.

[handlewanker]

Hi, I have always made dowel pins from high carbon steel, commonly known as silver steel or drill rod in the as supplied state, not hardened.......you can hit these with a hammer (with care) and also drive them out with a hardened pin punch......soft dowels have no use in a location situation and for all practical purposes are totally useless.

Provided you have a through hole, or ability to drill a small knock out hole behind the dowel for extraction purposes, the removal of a dowel is an easy business.......when dissasembling parts you always drive the dowels out of the part to be removed and down into the base part, leaving the dowel in place below the surface, (provided you have access to the rear end).

When the two parts are ready to be reunited, the dowel is punched up so that it is about 1mm above the surface of the base part....this enables you to locate the part on the dowels without the risk of burring the top of the dowel if misalignment has occurred.......the top part is then tapped down onto the dowel with a copper or soft hammer, screws fitted and nipped up and the dowels punched fully up from the back side........the screws are then tightened fully.

If you remove the dowels completely you risk having one or more dowels of slightly different diams in the wrong holes due to a previous doweling operation that went oversize.....then you will stuff up bonza!

Dowels should NEVER be fitted into a blind hole, IE, one where there is no access to the rear side where you cannot remove them prior to dissassembly of the two parts....it is practically impossible to seperate two halves of a job that have been doweled together without first removing the dowels.

In the case where the base is too thick to allow rear access to the dowel, the dowels are drilled and tapped in the top end for a screw to allow a drop or slide hammer or dowel jack to pull them out.

There is nothing more satisfying than driving a dowel into a job when it has been correctly fitted.

A roll pin has no place in the tool room....EVER........it is a production assembly locating device, and cannot be regarded in the same class as a dowel pin......people who use roll pins in place of dowels for toolmaking should be hung on barbed wire and left to rot....LOL.

I've seen many people assemble the two halves of a job with screws loosley in, insert the dowels from the top and punch them down.....often shaving the bottom end of the dowel and/or burring the leading edge of the hole in the base.

This method will work OK if the dowel has a small chamfer on one end.....the top of the dowel is domed to stop the corners being burred over by the hammer or punch.

Hardened dowels are not often used due to the fact that they come in set lengths and after hardening must be ground to size and are therefore much more expensive than straight forward cut to length as reqd silver steel dowels.

"Re-tightening" dowels that have gone loose in their holes is an occupation that those with dubious qualifications apply whenver the occasion arises....... and when nobody is watching them.

Loctite is the first choice......totally useless when the dowel is removed.

Peening the top of the hole with the round end of a ball peen hammer is the most favourite.

I once saw a hole "re-tightened" by someone driving an allen key into it to burr the inside and raise the metal up.......you can also use an "easy out" stud removel tool to spiral into the hole and burr it up........all bodge methods.
Ian.

[juergenwt]

Handlewanker - I agree with most of what you are saying. Having worked a lifetime as a tool and die maker in manufacturing (Germany and US) I can tell you that today nobody makes his own dowel pins unless something gets screwed up and a special size is required. Oversize dowel pins are available for purchase. Every Tool and Die Maker hates those and the special made once. Dowel pins used in today's manufacturing are all made to standards. Either DIN or ANSI etc. and are one of the cheapest components available.
All dowel pins used in manufacturing today have a radius on one side and a chamfer on the other. All, except the very cheap once or some made from special materials like stainless steel or wood or what have you, are fully hardened.
Your description on how to use a dowel pin and how to assemble components is right on. That is the way it is done.
Feels good to hear from a real professional - regardless of age. Juergen

[christinandavid]

A couple more handy dowel hints. Ream top 2mm or so of the hole about .05mm to 0.1mm bigger to guide your dowel in square when you fit it. When using dowels to assemble tooling, position holes offset to bolt hole pattern so tooling can only go together one way (same concept can be applied when locating parts). If using dowel pins to locate through holes in part, only one full diameter dowel is required. A second dowel is used to control the angular orientation of the part only, and is therefore ground or milled to a diamond shape and oriented so that the remaining portion of full diameter simply controls the angle of the part. Removing this 'redundant' location eases loading and allows tight fit on hole while reducing the need for the part to have holes with perfect positional accuracy.

DP