How does on press in small pins straight?

[RJSakowski]

Good point on the pin trapping air. I'll try making a flat on the pin to let the air out. I could drill further so the holes become through holes, but that's like gun drilling. Afraid that the hole would wander from true due to the high length to diameter ratio.

Pressing a 2mm pin 6mm deep into a 7mm deep hole would result in 7 bar of pressure or around 100psi. A 2mm pin has a cross sectional area of .005 sq. in. resulting in a force of .5 lbs. Negligible. However, if there is lubricant in the hole, all bets are off.

 

[WobblyHand]

Pressing a 2mm pin 6mm deep into a 7mm deep hole would result in 7 bar of pressure or around 100psi. A 2mm pin has a cross sectional area of .005 sq. in. resulting in a force of .5 lbs. Negligible. However, if there is lubricant in the hole, all bets are off.

I didn't think that the pressures would be high for captured air in a correctly sized hole. I think however, the drilled hole is too small and I'm shaving off material which might be filling the bottom of the hole. I did run a pipe cleaner in the holes to clean out any lubricant so I don't think I had hydraulic lock. Next time I'll use compressed air to make sure the holes are super clean.

Have to say this has been an interesting experience. This little wrench has been a bit more difficult to make than I anticipated.

 

[RaisedByWolves]

Pressing a 2mm pin 6mm deep into a 7mm deep hole would result in 7 bar of pressure or around 100psi. A 2mm pin has a cross sectional area of .005 sq. in. resulting in a force of .5 lbs. Negligible. However, if there is lubricant in the hole, all bets are off.

I had to make several gauges for engineering and reamed .001 under holes(only reamer we had) for 1/8” dowel pins to be pressed in.

They went in so tight the vise was making noises pressing most of them on. We were laughing and joking about it but didn’t think much of it.

These pins were pressed in to the depth of the slot they were located in (go/nogo gauge) so I knew they were right and handed them off to engineering.

Monday morning I got called to my bosses office with him wanting to know why the pins were all at different heights as he knows I’m particular about details.

Suffice it to say I was floored to see that 3 out of 8 pins were proud of the slot by varying degrees.

I took him and showed him what I did and damn if one of the pins came back out immediately with another following along as we were standing there.

I released them out the back with a #60 drill and they pressed in fine and are still in service.

I knew full well there would be a pressure build up, but no way did I expect this to happen.

 

[WobblyHand]

I had to make several gauges for engineering and reamed .001 under holes(only reamer we had) for 1/8” dowel pins to be pressed in.

They went in so tight the vise was making noises pressing most of them on. We were laughing and joking about it but didn’t think much of it.

These pins were pressed in to the depth of the slot they were located in (go/nogo gauge) so I knew they were right and handed them off to engineering.

Monday morning I got called to my bosses office with him wanting to know why the pins were all at different heights as he knows I’m particular about details.

Suffice it to say I was floored to see that 3 out of 8 pins were proud of the slot by varying degrees.

I took him and showed him what I did and damn if one of the pins came back out immediately with another following along as we were standing there.

I released them out the back with a #60 drill and they pressed in fine and are still in service.

I knew full well there would be a pressure build up, but no way did I expect this to happen.

These pins are tiny at 1.98mm and I have a lot of interference, about 0.05mm or so (0.002"). It wouldn't surprise me if the swarf sheered from the walls and the small remaining hole depth are giving me trouble. Some pins look fine, others are smooshed enough so that they are greater than 2mm in diameter. I know I drilled all the holes to the same depth, within 0.1mm. (7.0-7.1mm) Pins are 12L14 from McMaster (via Germany). The pins were pressed in an arbor press using the center boss as the stop, so they should be set to the same depth.

Looks like I need greater depth holes and less interference. Unfortunately I can't drill through the part (I think) it's 25mm long, which is really deep at sub 2mm diameter.

 

[RaisedByWolves]

These pins are tiny at 1.98mm and I have a lot of interference, about 0.05mm or so (0.002"). It wouldn't surprise me if the swarf sheered from the walls and the small remaining hole depth are giving me trouble. Some pins look fine, others are smooshed enough so that they are greater than 2mm in diameter. I know I drilled all the holes to the same depth, within 0.1mm. (7.0-7.1mm) Pins are 12L14 from McMaster (via Germany). The pins were pressed in an arbor press using the center boss as the stop, so they should be set to the same depth.

Looks like I need greater depth holes and less interference. Unfortunately I can't drill through the part (I think) it's 25mm long, which is really deep at sub 2mm diameter.

Any reason you’re not using dowel pins?

 

[WobblyHand]

Any reason you’re not using dowel pins?

They are undersized 2mm dowel pins. https://www.mcmaster.com/97049A203/

I could have bought 18-8 stainless dowel pins. https://www.mcmaster.com/97049A103/ but they were $2 more.

 

[WobblyHand]

Well, I can use this experience to collect more tools... Just received some 1.95mm drills, unfortunately in jobber size, so I will have to choke up on the bits. Eventually a 1.95mm reamer will arrive, but I'm a bit wary about that. Been burned on reamers, so I mic them upon receipt.

Been thinking about my next move. I sort of guessed (I did measure it, but there's a bit of uncertainty,) the hole circle diameter was 11mm, but maybe it isn't. Need some close fitting pins to measure this. The undersized dowels are too loose for this. I've never turned anything that small, what should I watch out for?

Then I'll do some peck drilling at that measured difference for just two holes and check I got the distance right.

 

[OTmachine]

Use HSS tool bits, preferably Mo-Max to turn pins. Cuts rather than pushes as Carbide does.

 

[Advil]

I would go with hardened dowel pins. You could be having trouble with the pins listed so far being too soft.

Try this list, 4140 alloy, hardness Rockwell C50, metric 1.5mm or 2mm pins:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

And another vote for a lot less interference fit for this project. Shoot for .001". Alternatively possibly a tight slip fit or very light interference fit and some Loctite 609. At least no chance of getting air trapped that way.

 

[Parlo]

Polish the pins to a taper for around 3/4 the length of engagement then have tha last 1/4 as the press fit. Don't faff about with the hole diameter unless you are using expensive odd size reamers. It's always easier to polish a pin to tenths to fit a hole than to try to machine the hole to the same fine tolerance. As said before, always have a flat for air release or have a deeper hole if it is blind. Standard dowel pin / reamer combination is the way to go. Always have a nice smooth chamfer or radius on the leading edge.