Boring bar sizing

It isn't just about fitting the tip in the hole - you gotta' be able to get the chips out. Initially, it can be a tight squeeze but as the hole opens up the chips eject easier.

No, the tip is not on the centerline of the work. It is raised about 0.005 - 0.010 above the centerline to offset tangential forces.

Normally, the flat on top of the tool is horizontal; this is called zero radial rake and allows for as much clearance as the relief angles under the tool provide. This relief under the cutting edge is important because as tangential cutting forces are generated the tool is pushed down and may contact the work. This is why you cannot use too large a tool in a tiny bore; you need to account for cutting forces and how they will affect the tool. This is also why carbide makes the best material for boring bars. It's modulus of elasticity is the stiffest of the common boring bar materials and will be least affected by tangential forces.
 
.1875" is not that small of a hole. A .0005" to .001" interference fit is about right. Much over that the bearing may get tight depending on the wall thickness around it.

I would use this boring bar. You need a little clearance for chips. Pre-drill with a spot drill then a #14 or #15 drill and then bore to final dimension. If I were doing a lot of these I would put the compound at Zero (parallel to the x-axis), keep the Z axis snug, lock the x-axis, put a 0-4-0 TDI against to tool post and use the compound to repeatably set the final bore depth.

I would not use a reamer unless your tail stock/drill chuck is dead nuts concentric to the spindle. Also most reamers have too large a chamfer for small bearings to seat fully to the shoulder.

In a pinch you could use a one or two flute 1/8 in end mill for a boring bar.
 
Just so much to learn! Honestly, it's all a bit overwhelming. You guys are really a wealth of info. Much appreciated guys!
 
I would just grab a 1/4 " tool bit and grind a bar out of it. For that depth it will be easy. Just FYI, Bronze tnds to spring back a bit when cutting or pushing a ball into it. You don't need a lot of interference.
 
Boring bars are the easiest tool to size.
If it will not fit into the hole it is to big (Minimum bore diameter) if it will not cut to depth it is to short (Depth/Length of cut) if it still does not perform and both of these parameters are met it will then take a bit of work.

A good place to start with a carbide tool at that diameter would be 200 SFM in aluminum or free machining brass, about 4000 RPM's for a bore that shallow.
How many parts is the big question when buying such tools.

As a sidenote, you will find that measuring such a feature will cost more then the tools used making it. You do have a dial bore gauge for that diameter do you not?
 
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A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.
Img_1921.jpg


I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.
Img_7597_zpscb8b5dd7.jpg


Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544
 
wildo said:
4000 rpm!? Is that correct??
Click to expand...
Yes, that is the low side however, 200 SFM is low for such materials with carbide tooling.
Read this: http://www.bravobronze.com/info/blog/details/use-our-c360-free-machining-brass-machining-guide
300-1000 SFM recommended for 360 brass, I calculate by hand but a handy cutting speed calculator may be found here.
http://www.carbidedepot.com/formulas-turning.htm

I do not use such speeds on lathes with jawed chucks because the jaws turn the coolant into mist.

Currently running 3/8" steel rounds, face turn and groove on both ends, 1500 RPM's in an 8" 3 Jaw chuck. A collet chuck does not fling coolant everywhere

500 parts 33 3/4" long. I could turn them at 3000 RPM's but it would mist the entire shop in coolant from the chuck/fan. Also a .5" deep 10-32 thread in one end, estimated lathe time is 91.4 hours.
 
A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.
Img_1921.jpg


I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.
Img_7597_zpscb8b5dd7.jpg


Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544
 
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