JRD77VET and other machinists, question for you.

[CertInsaneC5]

Today at work, one of our machinists was reaming out some 12mm dowel pin holes, in aluminum, that had gotten plated by mistake, putting them undersized. No big deal, it happens. The cleaned up holes when measured with gage pins, gaged correctly, except you could rock the "go" pin back and forth slightly. :skia:

We next checked them with a bore gage, and they are in tolerance at the top of the hole and .005" bigger at the bottom of the hole than at the top. WTF? I called BS and we set up our Sunnen bore gage. Same thing. They are not ovaled out or at an angle. How in the hell did this happen? This is going to bug me all weekend. :leaving:

[DAB]

i normally work to +/- 1/32" :shrug:

[Ol Timer]

i normally work to +/- 1/32" :shrug:

We woodworkers are fine with tolerances we can see with our tired old eyes. Machinists get all crazy to the right of the decimal. :)

[Blademaker]

We woodworkers are fine with tolerances we can see with our tired old eyes. Machinists get all crazy to the right of the decimal. :)


Make folding knives.......I'll show you a level of crazy..........

[CertInsaneC5]

We woodworkers are fine with tolerances we can see with our tired old eyes. Machinists get all crazy to the right of the decimal. :)

+/- .0004" on the holes in question.

[JRD77VET]

Today at work, one of our machinists was reaming out some 12mm dowel pin holes, in aluminum, that had gotten plated by mistake, putting them undersized. No big deal, it happens. The cleaned up holes when measured with gage pins, gaged correctly, except you could rock the "go" pin back and forth slightly. :skia:

We next checked them with a bore gage, and they are in tolerance at the top of the hole and .005" bigger at the bottom of the hole than at the top. WTF? I called BS and we set up our Sunnen bore gage. Same thing. They are not ovaled out or at an angle. How in the hell did this happen? This is going to bug me all weekend. :leaving:

+/- .0004" on the holes in question.

Before I answer with what I think may have happened, a few questions.

What type of "plating"?

Blind holes or thru holes?

What did he use to open the holes? If a reamer, straight flute or spiral?

Jeff

[CertInsaneC5]

Before I answer with what I think may have happened, a few questions.

What type of "plating"? Black anodize

Blind holes or thru holes? Blind

What did he use to open the holes? If a reamer, straight flute or spiral? Reamer, straight flute.

Jeff

In almost 30 years of machining experience I have never seen this. Has me completely stumped.

FYI. The holes are about 20mm deep.

[JRD77VET]

In almost 30 years of machining experience I have never seen this. Has me completely stumped.

FYI. The holes are about 20mm deep.

I'd bet a dollar the machinist came down against the bottom of the hole. The black anodize is much harder than the aluminum and the chips wallowed the hole out as the reamer made contact with the bottom. :yesnod:

Before I got an adjustable ( expanding ) reamer here at home for making Cub Cadet drive hubs, I would take my 5/8" reamer and purposely bottom it against the bottom of the drilled hole to open up the hole from .625 to .626/.627 so the 5/8" driveshaft slipped in easily.

The holes in your aluminum part are close to two diameters deep so there were plenty of harder than parent material chips to build up. The machinist could have been light on cutting fluid too since it was a finished part.

[CertInsaneC5]

I'd bet a dollar the machinist came down against the bottom of the hole. The black anodize is much harder than the aluminum and the chips wallowed the hole out as the reamer made contact with the bottom. :yesnod:

Before I got an adjustable ( expanding ) reamer here at home for making Cub Cadet drive hubs, I would take my 5/8" reamer and purposely bottom it against the bottom of the drilled hole to open up the hole from .625 to .626/.627 so the 5/8" driveshaft slipped in easily.

The holes in your aluminum part are close to two diameters deep so there were plenty of harder than parent material chips to build up. The machinist could have been light on cutting fluid too since it was a finished part.

I would have thought that as well. But the top of the hole is in tolerance?!? It was a ~ 6" long tool. I checked the spindle and the vice he was using to see if there was play in them. No problems there. He was using good cutting fluid and spraying off the reamer every time. Anodizing is very abrasive. So watching out for the tool dulling is a norm here. There was no gauling at the bottom of the hole. We have done this 100's of times with no problems. If the reamer at this length was wobbling on the bottom of the hole I can not see how it would not also open up the top of the hole?

[JRD77VET]

I would have thought that as well. But the top of the hole is in tolerance?!? It was a ~ 6" long tool. I checked the spindle and the vice he was using to see if there was play in them. No problems there. He was using good cutting fluid and spraying off the reamer every time. Anodizing is very abrasive. So watching out for the tool dulling is a norm here. There was no gauling at the bottom of the hole. We have done this 100's of times with no problems. If the reamer at this length was wobbling on the bottom of the hole I can not see how it would not also open up the top of the hole?

Chips in the slurry at the bottom abraded the hole at the bottom. I've had variation in bores where I've bored across weld seams and had that section measure different.

It's one of those times when what worked before didn't work this time.

He had the reamer held "long" which is a big plus. You say the spindle and the vise were good.

The only thing I would find fault was not catching it after the first hole. Maybe he did check the first hole with a pin but didn't check for wobble. ( I don't want to throw him under the bus since I wasn't there to know exactly what happened or know his work record. Sometime the best machinists have "shit happen" to them )

[CertInsaneC5]

Chips in the slurry at the bottom abraded the hole at the bottom. I've had variation in bores where I've bored across weld seams and had that section measure different.

It's one of those times when what worked before didn't work this time.

He had the reamer held "long" which is a big plus. You say the spindle and the vise were good.

The only thing I would find fault was not catching it after the first hole. Maybe he did check the first hole with a pin but didn't check for wobble. ( I don't want to throw him under the bus since I wasn't there to know exactly what happened or know his work record. Sometime the best machinists have "shit happen" to them )

He was at as much of a loss as we were to what went wrong. We're only talking about taking about .001" of plating out of the holes. He is in no trouble at all and has done this operation many times. Basically, plunge in then back out. No delay. I wonder if these holes were that way before plating. A bad endmill grind could do this. It they were helical milled instead of reamed. I have to check Monday with the plant that makes these parts. I would be amazed if they are doing this with a mill on H7 tolerance holes.

[JRD77VET]

He was at as much of a loss as we were to what went wrong. We're only talking about taking about .001" of plating out of the holes. He is in no trouble at all and has done this operation many times. Basically, plunge in then back out. No delay. I wonder if these holes were that way before plating. A bad endmill grind could do this. It they were helical milled instead of reamed. I have to check Monday with the plant that makes these parts. I would be amazed if they are doing this with a mill on H7 tolerance holes.

I (wrongly) assumed that you made the parts and had a problem with the anodizer not masking the holes. Yes, a bad grind on an endmill to circular interpolate could be the original problem.

A new quality mill could hold those tolerances with good tooling but ........

[CertInsaneC5]

I (wrongly) assumed that you made the parts and had a problem with the anodizer not masking the holes. Yes, a bad grind on an endmill to circular interpolate could be the original problem.

A new quality mill could hold those tolerances with good tooling but ........


:iagree: Just that. Why would they increase their cycle time by doing this? We are talking 20 parts with 2 holes each. ~$300 per part as well. Something stinks here. I suspect it's not us. :cert:

[markids77]

New tooling? Suspect a substandard ream, possibly flexure/ tool wobble from too fast entrance speed?

[CertInsaneC5]

New tooling? Suspect a substandard ream, possibly flexure/ tool wobble from too fast entrance speed?

That would make the hole too big at the top. Not the bottom. We are talking about a 12mm reamer here. About a half inch for you metrically impaired folks. Besides the reamer always follows the hole for sizes in this range. :cert:

[JRD77VET]

:iagree: Just that. Why would they increase their cycle time by doing this? We are talking 20 parts with 2 holes each. ~$300 per part as well. Something stinks here. I suspect it's not us. :cert:

Most likely a reduction in cycle time. :yesnod:

Let's say they are using a 5/16" carbide two flute endmill in a newer high speed mill. 2000 SFM is 25,000 RPM and if you give it a feed per tooth of .0005 ( way slow ) that is a feed rate of 25 inches per minute.

Maybe you need to get more thorough inspection reports from your supplier :yesnod: