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View Full Version : Ultra basics: Why are reamer shanks so loooooong?



Arthur.Marks
06-15-2010, 10:52 PM
I feel a little stupid asking the question :o
Just exactly why are the flute and shank lengths so generous in comparison to diameter? The standard ratio is huge!

Mcgyver
06-15-2010, 10:55 PM
I believe there is a standard governing this, may be in Machinery's Handbook. afaik its to ensure they have enough flex.....the reamer is supposed to accurately follow the hole not the path the drill chuck's pointing it in which could be several though off or eccentric.

Paul Alciatore
06-15-2010, 11:26 PM
I believe there is a standard governing this, may be in Machinery's Handbook. afaik its to ensure they have enough flex.....the reamer is supposed to accurately follow the hole not the path the drill chuck's pointing it in which could be several though off or eccentric.

Oh yea! I have a one inch reamer and it is less than a foot long. I guarantee it will not flex much. It would have to be several feet long for that to work.

I guess that works if the reamer is under 1/4" or so. But I suspect it if for reach, not flex. Perhaps for deep holes.

lakeside53
06-16-2010, 12:02 AM
Long can be good, but can also be a PITA. I've had to cut many so I have enough working height under my BP spindle.

For the most part I'll go with the self aligning "flex" theory though...

Black_Moons
06-16-2010, 12:08 AM
Paul Alciatore: Does nobody believe that all these tools are actualy all made of rubber? (At least, on the scales we deal with)

I bet if you chuck that 1"x12" reamer up, put a TDI on the tip of it and push, 10lbs will easly deflect the reamer 0.002", Enough to make aligning it up with an existing hole MUCH easyer.

danlb
06-16-2010, 12:36 AM
It occurs to me that keeping a long reamer aligned with the hole would be easier than doing the same with a short one. You can spot the .010 per inch that you are low much easier at 10 inches than you can at 2 inches.


I could be totally off base.

Dan

PeteM
06-16-2010, 12:59 AM
The longer shaft allows reaming a deeper hole. Lot cheaper adding length to the shaft than the flutes. Also easier to sharpen.

lakeside53
06-16-2010, 01:04 AM
This type of reamer (chucking) is primarily re-sharpened only at the face of the tip - not the flutes. Sharpening the flutes is possible, but that will change the dimension.

Mike Burdick
06-16-2010, 01:48 AM
Arthur.Marks,

Actually, that's a very interesting question!

As a side note, I'm glad they are long as I make boring bars from them - especially the smaller diameters.

.

DR
06-16-2010, 08:25 AM
The length is most likely for reach. If shorter is needed, cut it off. Much easier to shorten than lengthen.

Or, buy stub reamers.

Having a reamer flex to follow a hole would not give accurate size. If the reamer needs to follow a hole, use a floating holder.

Mcgyver
06-16-2010, 11:50 AM
Oh yea! I have a one inch reamer and it is less than a foot long. I guarantee it will not flex much. It would have to be several feet long for that to work.

I guess that works if the reamer is under 1/4" or so. But I suspect it if for reach, not flex. Perhaps for deep holes.

you don't think a 1" reamer is going to flex? everything made of metal flexes. I'm only talking a few thou; like as when lathe tailstock is a bit low or the drill chuck has a couple of thou run out. I've seen it numerous times with the reamer is visually turning eccentrically but upon starting the hole straightens out - something's flexing.

i can't buy the deep hole idea as why are reamer standards (length is ANSI defined) so out of step with standard drill lengths...also its a lot of extra material for the once in a life time need for a 6" deep 3/8" reamed hole. I think if it was for depth, there'd be a rarer extra long set and standard reamers would be the length of say jobber drills

I can't remember where i got the flex bit from, or maybe i just made it up....without being able to remember a source i sent an email to Dormer (butterfield) hoping they can shed some light ....i'll post if hear anything

Fasttrack
06-16-2010, 12:04 PM
I can't remember where i got the flex bit from, or maybe i just made it up....without being able to remember a source i sent an email to Dormer (butterfield) hoping they can shed some light ....i'll post if hear anything


I heard the same thing on this forum awhile ago. I'm very interested to hear what Dormer says.

I've seen solid carbide reamers that are short and stuby. I suppose one could argue that these need to be used with a floating holder while the long HSS ones don't need the floating holder, despite the fact that they are both marketed merely as "chucking reamers".

Mcgyver
06-16-2010, 12:08 PM
I heard the same thing on this forum awhile ago. I'm very interested to hear what Dormer says.

maybe you heard it from me :D

lakeside53
06-16-2010, 12:13 PM
Maybe they are long (and flexible) to track the work better when mounted in the typical drill chuck...? I know mine have a heck of a lot more run-out than my colletts.

saltmine
06-16-2010, 12:15 PM
I often wondered about this myself. I have two sets of reamers, and sometimes run into problems getting enough clearance between the work and the quill on my "mini-mill" because the shank of a reamer is way too long.
Several times I've ended up clamping the part to a faceplate or a four-jaw chuck and reaming with the lathe's tailstock. Worst case scenario I've had to resort to clamping a part in a vice and reaming it with a cordless drill.... I know, it's not good "shop etiquette", but it works. ( My brother and I reamed to size 8 wristpin bushings for a Ford flathead V-8 once, with a vice and a cordless drill. The engine is still running perfectly with over 40,000 miles on it since)

I've even considered cutting a couple of inches off the shank of some of my reamers. (I'll probably have to cut them off with a cutting torch, since they seem to be pretty hard steel)

lakeside53
06-16-2010, 12:26 PM
Torch? They cut very easily with one of those thin (30 to 50 thou) abrasive cutting disks in a die grinder.

Stuart Br
06-16-2010, 01:53 PM
Why not use a reamer in a cordless drill? This was effectively what was done as standard practice when I was in the aircraft industry 20+ years ago. We were using a guide bush to ensure that the reamer was square to the hole though. After all you can't put a huge chunk of airframe onto a Bridgeport :D
I did a stint in the airframe assembly shop as part of my apprenticeship and we were bolting together engine pylons for Rolls Royce powered Boeing 747's. Bolt holes were drilled with a jig. We then reamed to size with a large slow speed air drill using the guide bush. Each hole was then checked and signed off by an inspector before a bolt was allowed anywhere near it. Any holes that failed had to have an exception raised and design authority gained to open up the hole to the next size. Another interesting point was that Boeing didn't allow any form of countersink on the hole as this could subject the bolt to bending stress instead of the designed tensile stress. All that was allowed for deburring was a scrape to surface level.

Stuart

MuellerNick
06-16-2010, 03:09 PM
It's an anti-Bridgeport-conspiracy!


Nick

jugs
06-16-2010, 06:01 PM
It's an anti-Bridgeport-conspiracy!


Nick

I bet Sir John's behind it.
john
:)

BobWarfield
06-17-2010, 10:41 AM
Nah, you don't want to deflect the reamer or it will make an oval hole and be more prone to chatter. If the hole and spindle axis are not concentric, you should use a floating holder.

Dormer has a reamer handbook that's worth looking through. They'll tell you, for example, to choke up on the reamer as much as possible and that stiffer reamers (carbide) will give you a better finish with less chatter.

Also, not all reamers have those relatively short flute lengths relative to shank length. More expensive ones will often have longer flutes. The flutes are the expensive part to make, so that's where the toolmaker will want to economize. The DIN specs call out such longer flute proportions, see page 58, for example, of the Dormer Handbook:

http://www.mbmpraha.cz/pdfkatalogy/Dormer/Hbook.pdf

Cheers,

BW

Paul Alciatore
06-18-2010, 02:37 AM
Paul Alciatore: Does nobody believe that all these tools are actualy all made of rubber? (At least, on the scales we deal with)

I bet if you chuck that 1"x12" reamer up, put a TDI on the tip of it and push, 10lbs will easly deflect the reamer 0.002", Enough to make aligning it up with an existing hole MUCH easyer.

Yea, but how would you know if it was the reamer or the chuck that was the real rubber?