Dowel Pins

[Mr.Chips]

I would like some information about the installation and use of dowel pins.

Are the dowel pin holes drilled after the pieces are bolted together and aligned?

In many situations the work may be too big to fit in the drill press, what do you do then?

Are the holes in both pieces the same, or is one of the holes reamed slightly larger so it could be disassembled?

If you are using a 1/4" dowel pin, what size hole should be drilled for it? And are both holes reamed?

I'v been a hobby wood worker for years and this CNC hobby has expanded my areas of interest into metal.
Hager

[DavidB]

There are a lot of variables here.If the steel can be mounted together first then drilled and reamed together the alignment woukd be perfect.The holes are the same dia in both piece uasual a H7 fit.On a 1/4 dai hole i would pre drill 0.008-0.012" smaller then ream with oil.If you where to pitch both out sepperate i would pre drill and then spot with a cutter,then ream.
If the material is to hardened the reamed hole is to finished then polished if needed after heat treat.


Hope this helped

[Mr.Chips]

David Uhhhh.

Whats a H7 fit?

Do all reamers have an adjustment screw in the bottom to expand the reamer, or am I thinking about something else?

Are reamers tapered, if not how do you get them in the hold.

Told you I was a wood worker, sorry for the details.
Hager

[DavidB]

You can get hand reamers or machine reamers.They are parallel all the way and there is no adjusting screw at the bottom.H7 is a standard that is tied to a hole size tolerance.A reamer will only follow the previous hole so thats why if you do each piece seeparate the pitching is important.Try and always chamfer the hole before reaming aswell as this provides a lead.

[Klox]

Hager,
You get different types of reamers. You get adjustable reamers,
parallel shank reamers that can be held in a drill chuck (preferably in a collet) and tapered (morse taper) shank reamers.

A H7 tolerance means a clearance larger than the dia of the hole.

You can ask your tool suplier for charts on tapping & drilling sizes as well as technical info on tolerances regarding reaming.

Klox

[Mr.Chips]

Thanks for the information, I'd seen dowel pins used and wasn't sure of the details.
Hager

[HuFlungDung]

A method that I find quite economical, is to use a single reamer that allows maybe .0005 to .001" clearance, and ream right through both holes. Then, if there is a preferred side, put a drop of loctite on the pin for that side and glue it in.

Otherwise, you can buy paired reamer sets in .001" over/under for reaming a press fit hole for the pin, and a clearance hole for the easy fitting side.

[Mr.Chips]

Thanks HuFlung,
You answered one of thoes unasked questions.

I'm thinking I would want to leave the pins in the main body and have the minor piece come free when you want to take it apart.

In typing this I realized that, if you use two dowels in one piece you'd better have holes that are really perpendicular to the surface if you want to be able to take it apart.

There's so much to learn in metalworking.
Hager

[balsaman]

Some dowels have a hole in one end that is tapped. You can use this hole to insert a bolt and use a small slide hammer to remove the dowel before dissasembly.

E

[wjbzone]

I make a lot of tooling at work using dowel pins for assembly. I usually have one piece with a blind hole (not through) and mating piece with a through hole.

I make the blind hole a slip fit (Ø0.251 -0.253 hole for a Ø0.250 dowel) and the through hole a press fit (0.249). I can remove the press fit pin easily with a smaller pin.
Bill

I drill / reame each piece on a bridgeport or cnc before they are assembled. If you don't have the accuracy to align the pins, make your slip fit holes a little larger.

[Mr.Chips]

My metal working tools are very limited and primitive.
Have a heavy duty Rockwell drill press that’s probably 40 years old, I bought it for $20 as salvage equipment, it had been converted to a lab mixer and the table was gone. I made a MDF box that is bolted to the slots in the base. Checked the perpendicularity to the chuck and it's .004" out on a 10” circle. OK for me. Been looking for a table with a 2.75" post for months. Found a complete floor model DP at the recycle yard but the head and motor were bad and they wouldn't let me just buy the post.

Cut Alum on my craftsman band saw, and table saw. Starting to collect taps and dies as I need them.

So after reading this thread I don't think I'm ready for doweling. I'm hoping my machine will be good enough to do the alum machining to make my second machine.

I’ll run some test pieces and take them to my old Co. and measure them on the computerized measuring equipment. From there I’ll be making decisions on my machine.
Hager

[HuFlungDung]

Mr Chips,

If you like, you could simply drill the holes with standard twist drills and use rolled spring pins to keep stuff lined up. These pins come in standard fractional inch sizes, nothing special required for drill bits.

You do need a through hole to knock them out when disassembling stuff though.