Reamer questions

[graham-xrf]

There are so many types..
I guess what makes a "hand reamer" vs "chucking reamer" is the provision of flats to get a spanner in there, but here, the question is about spirals. I get it that a reamer with straight flutes is probably OK, and with spirals, it's better, but what is the wisdom about the direction of the spirals?

Here is what I mean. This is a right-hand cut with left hand spirals.



Then, you can get them get them go the other way. Right-hand cut with right-hand spiral - unless I mistake, and the whole thing cuts anti-clockwise!


Of course, one can get straight flutes. I guess they cost less to make, but I have my doubts about this deal.
The whole set of 10 pieces 3mm thru 12mm in H7 grade can be had for £14.99, which converts to $21.13. Also, they seem "short", which might be a good thing in a mill with not much Z-Axis height.


Of course, I be the guy who bought 105 so-called "cobalt" drill bits that would disgrace even the rust they will end up as in the landfill, so if the deal looks too good to be true, it probably is, but this is not about pricing. I want to know what you experienced folk go for when choosing reamers.

I see also "adjustable" types. How good are they?

 

[mmcmdl]

 

[JRaut]

Don't forget about the David Brown-type adjustable, floating reamers!

Those things are pretty slick.

And I hear that *ahem* someone *ahem* is selling a nice set of them over on the buy/sell section of this forum:

https://www.hobby-machinist.com/threads/anyone-interested-in-david-brown-adjustable-floating-reamers.93080/

In addition to the flats, the first 'diameter' or so of a hand reamer has a slight taper to aid in getting it straight in the hole. Conversely, a chucking reamer has a well defined short cutting chamfer at the end, often at about 45* or so.

Spiral-fluted reamers are a must-have if you're trying to ream out a bore with a keyway. The flute direction dictates which way the chips are pushed/pulled, but I'm not sure beyond that why someone would opt for left/right spiral. Vast majority of my reamers have straight flutes and I haven't ever had a problem.

I've got one of those cheap-o metric sets; the whole set cost less than a single high-quality reamer, so I figured I'd give it a whirl. Some ream on size, some over, some under. Kind of a crap shoot. But worth the $20 if you're only using them for the odd non-critical hole here and there.

 

[macardoso]

I've bought some *bargain* metric reamer sets from Ali-Express (mine probably looked worse than the link you showed). They cut pretty poorly and the wall finish is atrocious, but they do make holes pretty accurately so I keep them for use in a pinch.

I've only used chucking reamers with straight flutes on a mill or lathe, so I cannot comment much on hand reamers or spiral flute reamers.

 

[pacifica]

I might be missing something here-but I ream a hole when I need a precise diameter-say within a thousanths inch. So why get an inexpensive reamer that you can't trust to be accurate?
I also match a quality drill bit with the reamer so the reamer doesn't remove more than a hundredth inch of diameter.

 

[graham-xrf]

I might be missing something here-but I ream a hole when I need a precise diameter-say within a thousanths inch. So why get an inexpensive reamer that you can't trust to be accurate?
I also match a quality drill bit with the reamer so the reamer doesn't remove more than a hundredth inch of diameter.

The cheapo straight flute set in the picture was something I saw on eBay, allegedly H7, and with a "2 year warranty".
I absolutely agree! My preference is kit that I would never want nor need to invoke a warranty on anyway, and I was more interested in the preference choice between various types, such as spiral flute or not. I now think there might be more to hand reamers than just the flats for the wrench. Some part of the reamer length might also be slightly tapered.

In the allowance 0.01" in diameter between drill and reamer, it splits to 0.005" as the depth of cut the reamer finally removes, though I am not sure if any part of the reamer does a 0.005" cut all at once. I was interested that one can get slightly "under and over" sized reamers where one kind is to make a sliding fit, and the other size is a press fit for pins and dowels

 

[WobblyHand]

I bought a standard reamer in 1/2" from a reputable supplier. It gave a very nice finish. But it was so long, that I did run out of Z. Had to use the mill 1" higher than my max Z height to do the job. This was for a piece that was flush with the vise. When I use it again, I will cut off part of the shank, it is just too long for my mill. The reamer was 8" long, straight flute, APT brand. I have 11" Z height, there's a 2.5" high vise, and a chuck. So keep that in mind if you have a smaller mill (PM25).

 

[Flyinfool]

It all depends on the specific hole you are making.
I am referring only to right cut reamers, I have never seen a left cut and do not know a reason you would need one.

Straight make great general purpose reamers, but should never be used for an interrupted cut like a keyway. If it is a deep hole you may have to stop and clear chips since they will build up in the flutes. Just like a straight flute tap. This in and out and packing of chips can damage the already reamed surface,

Right or left spiral are needed for interrupted cuts or non interrupted cuts as you will never have one complete cutting edge fall into the keyway and make for a non round hole.

Right spiral will pull the chips up out of the hole, like a spiral tap or drill bit would, and is best for blind holes so that you can ream right to the bottom of the hole. But since the chips are flowing UP through the reamed hole they have a chance to scratch the reamed surface.

Left spiral are best for thru holes as they drive the chips deeper into the hole like a spiral point or gun tap would. This way there is nothing that can damage the reamed surface.

The long shanks are to allow some flex so that the reamer can more accurately follow the pilot hole. If you are going to shorten the shank it is best to drill then ream on a mill or lathe without moving the part. This means lots of switching bits and fewer machine moves. You will not want to drill all the holes and then come back to ream them.

 

[graham-xrf]

It all depends on the specific hole you are making.
I am referring only to right cut reamers, I have never seen a left cut and do not know a reason you would need one.

Straight make great general purpose reamers, but should never be used for an interrupted cut like a keyway. If it is a deep hole you may have to stop and clear chips since they will build up in the flutes. Just like a straight flute tap. This in and out and packing of chips can damage the already reamed surface,

Right or left spiral are needed for interrupted cuts or non interrupted cuts as you will never have one complete cutting edge fall into the keyway and make for a non round hole.

Right spiral will pull the chips up out of the hole, like a spiral tap or drill bit would, and is best for blind holes so that you can ream right to the bottom of the hole. But since the chips are flowing UP through the reamed hole they have a chance to scratch the reamed surface.

Left spiral are best for thru holes as they drive the chips deeper into the hole like a spiral point or gun tap would. This way there is nothing that can damage the reamed surface.

The long shanks are to allow some flex so that the reamer can more accurately follow the pilot hole. If you are going to shorten the shank it is best to drill then ream on a mill or lathe without moving the part. This means lots of switching bits and fewer machine moves. You will not want to drill all the holes and then come back to ream them.

Thank you! That makes complete sense. The cut is normal clockwise. The spiral can be either direction, depending which way you want to clear the chips out. I can see why the left hand spiral is the more prevalent. Through is the direction the reamer is going anyway, and why bring chips back onto your freshly cut surface unless a blind hole reaming forced the choice.