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Home > Main Forums > Gunsmithing Tools > reamer diameter relative to hole/chamber+other q's, Does a .500" OD reamer  make a .500" ID?
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Posted: Sep. 16 2004, 00:57 ET

Feels darn good to get back to these forums I've noticed how much this place has grown since I was last here. back the home shop stuff, does a 1/2" O.D. reamer produce an EXACT 1/2" ID hole? or is it undersized a few thousands?

My second question is: what makes chamber reamer so special? If I have a good solid cross slide with a super duper accurate Jacobs chuck thats been zeroed with ye old centerfinder or beter yet a DRO would that cut it? no pun intended. :)

Posted: Sep. 16 2004, 01:39 ET

#1 - Sure, as long and the reamer is straight, the lathe has zero run out and your tail stock is perfectly aligned.  Otherwise, no.

#2 - I'm not that talented, a bottle neck cut would be beyond my ken.  A mild taper like a 38 Super Auto or 9x23 can be done.  A chamber reamer is just simpler and cheaper.

Posted: Sep. 16 2004, 04:16 ET

much obliged, 38super.

I fell kinda silly 'cause I forgot the most important part of the second question, I meant to say: chamber reamer HOLDER not just chamber reamer, as in if I got my jacobs chuck as accurate as humanly possible and just swapped the centerfinder/dial I'm using to zero, with a chamber reamer for a rifle round like a .300 WSM or .22-250 roberts? I have to say thanks for the help, I was interested in tackling some home made multi-flutes, its nice to know some chambers can be cut without a chamber reamer though, I learn smothing new everyday here.

Posted: Sep. 16 2004, 15:10 ET

Brownells Gunkinks 1 has an article by Fred Huntington on using the Jacobs.  Do a search for Mike Bryant Gunsmithing, I believe he uses a shop made reamer holder.  Mike

Posted: Sep. 17 2004, 11:42 ET

I have used the chuck to hold a reamer many times. One of the floating reamer holders that I had would come back to center as soon as there was torque applied, the center not always being lined up with the center of the barrel. so I quit using it. I have plans to build one that will not be moved by torque, just need time to build it.

Posted: Sep. 17 2004, 15:40 ET

No worries gunsmithkid,

Just after setting up my ShopTask, I started playing with some stainless rod stock to build some compensators.  After much agnst I talked with a TRW master model maker who educated me on the how's n why's stainless sux.  

So if you're not sure, ask.  I continue to learn.

Posted: Sep. 17 2004, 21:49 ET

Thanks I think I get it now.

Why does stainless suck?

Is it beceause of machinabilty rating? I'd imagine putting some large diameter threads on would be a chore.

Posted: Sep. 18 2004, 12:30 ET

It's gummy due to the nickel content and will locally heat treat at the cut face.  HSS insert or cutting tool, slower revs and lighter cuts than mild steel.  Different cat, different skinning technique.  

This is just the lathe, wait til you use a mill. :O
I've used aerosol WD-40, diesel fuel, motor oil, aqueous cutting fluids (this stuff goes moldy, so dump and mix a new batch) .

Posted: Sep. 19 2004, 02:16 ET

Kid, to answer your original question. Reamers are ground to the exact size as stated on the reamer, there are reamers ground to .499 and .501 for loose or press fits. As to whether you get that is another thing as 38 super said if everything is right on it will give you what the reamer says, but that rarely happens given the type of tools we use and how we use them. The other part of the question is related to the inaccuracy of the machining processes we use. The chambering reamer holder is usually a "floating holder" this allows the reamer to move slightly and in doing so align itself (it's pilot ) to the bore of the barrel. Again if everything was dead on in the barrel and machine setup you could chuck the reamer in your PERFECTLY ALIGNED tail stock drill chuck and ream away. But this is the real world and if you just chuck the reamer in your foreign made drill chuck in your not so perfectly aligned tail stock the reamer pilot is going to try and follow the not so perfect barrel bore (remember this is the real world) and it will act like a boring bar. Sure it will chamber and it will look OK but it will most likely be an over sized chamber , due to the reamer being held rigidly and probably cutting on one side only.Have you ever drilled a hole in a chunk of stock in a lathe and had the drill start not quite on center? The resulting hole is bell mouthed and over sized.  Also there is no such thing as an super accurate Jacobs chuck, that's why they make reamers. Just my $.02 worth.



Posted: Sep. 19 2004, 04:35 ET

Gummy and self heat-treating mid machine process, that does suck, well now I know.

stractor, I think I get the reamer theory, the floating reamer holder gives the reamer enough "play" and movement to let the pilot guide the entire reamer into he pre-existing bore. now if I could only get a set of blueprints for a floating reamer holder......  


Posted: Sep. 19 2004, 10:55 ET

The barrel companys that I have checked with use 416 stainless which will machine much better. I use it for brakes and find that it is not bad to machine. It is magnetic but will not take cold or hot blue.

Posted: Sep. 19 2004, 11:34 ET

The idea when using the Jacobs to ream, is to let the reamer float in it.  I am not recommending it, as I have never used this method, but it is a technique that has been in use for decades, by some very talented 'smiths.  Check the references I gave, and you will have some ideas about making a Jacobs work.  Mike