# Boring .250" for 1" in 1144 steel



## martik777 (Aug 17, 2021)

I've been drilling 15/64 (.235") and boring out to .250 with a 5mm carbide end mill (as a boring tool)  but of course it flexes a little so it takes a lot of passes. Wondering if there is a better way. I need < .001" runout


----------



## BGHansen (Aug 17, 2021)

I'd look at using a boring bar to size or a reamer.

Bruce


----------



## mksj (Aug 17, 2021)

You can also use a screw machine stub drill or mechanics drill which is shorter and stiffer and less pron to walking/flexing, otherwise drill one size under 0.250 and then use a 0.250" reamer or stub drill. Start the hole with a center drill.








						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com


----------



## martik777 (Aug 17, 2021)

mksj said:


> You can also use a screw machine stub drill or mechanics drill which is shorter and stiffer and less pron to walking/flexing, otherwise drill one size under 0.250 and then use a 0.250" reamer or stub drill. Start the hole with a center drill.
> 
> 
> 
> ...



What is the maximum I can ream out and still be concentric within .001"?


----------



## Mitch Alsup (Aug 17, 2021)

The reamer only takes the hole to size and makes it round, it does little to guarantee concentricity.

Now, what you CAN do, is to make a hole of the proper diameter, and then mount the bar on the lathe using centers, and then turn the outside to size; and you are practically guaranteed to be concentric. {I had to do essentially this with some wheels I made:: ID = 0.246, OD = 0.459. I fought and fought trying to drill the hole after the OD and gave up. Drilling first solved the problem. Did I mention I love turning on centers.}


----------



## mksj (Aug 17, 2021)

Reamers are made for final sizing, not for significant material removal (often 1-2 thousandths). I use reamers often when I have some binding in holes and I have very close fitting parts. They are also available in + or - sizes in small incremental sizes if you need a specific clearance. I do applications with holes with various size drill rod that needs a close fit,  the clearance and alignment needs to be 0.001" or less over 2". Also depends on the material. Since the reamer cutting is 1.5" in the one below it should to  true, but it depends on how you do it. I would start with a short drills first and see if that works.








						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com
				











						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com


----------



## Asm109 (Aug 18, 2021)

Drill the hole, then take one or two passes with the boring bar. This will bring the hole concentric with the axis of the lathe, leave about .015 stock to remove. Use a reamer to bring it to size. Done.


----------



## MrWhoopee (Aug 18, 2021)

It's something Billy used to chant while dancing in front of his lathe: "bore then ream. bore then ream."


----------



## Mitch Alsup (Aug 18, 2021)

Asm109 said:


> Drill the hole, then take one or two passes with the boring bar.



Fitting a boring bar in a hole already less then 0.250" in size requires a really tiny boring bar.


----------



## Asm109 (Aug 18, 2021)

Yeah, but read post #1.  OP has a 5 mm boring bar that he was using to bring the hole to size.  Reamer does a much better job of that.


----------



## BladesIIB (Aug 18, 2021)

Take a .005" cut, let it flex.  Then take .005" from where you left off that cut, not from where it touches.  Measure and take half of what is left (from last cut setting) then you should have that same amount for a finish cut.  Once the bar flexes, just use that to keep measuring from, if you keep depth of cut consistent it should flex the same and get you to accurate size.  Could maybe even eliminate the second pass just take .007", measure, take half remaining then finish pass.  Most boring bars flex and leaving the flex in and taking two equal depth finish passes is how I typically get to my final size.


----------



## martik777 (Aug 19, 2021)

BladesIIB said:


> Take a .005" cut, let it flex.  Then take .005" from where you left off that cut, not from where it touches.  Measure and take half of what is left (from last cut setting) then you should have that same amount for a finish cut.  Once the bar flexes, just use that to keep measuring from, if you keep depth of cut consistent it should flex the same and get you to accurate size.  Could maybe even eliminate the second pass just take .007", measure, take half remaining then finish pass.  Most boring bars flex and leaving the flex in and taking two equal depth finish passes is how I typically get to my final size.



This is essentially what I'm doing. It doesn't flex much, maybe  .002". A razor sharp edge helps it cut consistently without a sudden overcut. 
No way to easily measure .250 so I made a couple plug gauges.


----------



## macardoso (Aug 19, 2021)

I agree, Drill, bore for concentricity and stock allowance (couple thou), then finish ream to size. 

0.001" on concentricity is pretty wide open IMO. A good reamer will not walk if the bored hole is of even marginal quality. The boring bar will clean up any walking from the drill.


----------



## BladesIIB (Aug 19, 2021)

martik777 said:


> This is essentially what I'm doing. It doesn't flex much, maybe  .002". A razor sharp edge helps it cut consistently without a sudden overcut.
> No way to easily measure .250 so I made a couple plug gauges.


Sounds like you have a good system then. 3 passes with the boring bar does not seem to excessive?  Maybe get that down to 2 if you are doing several and get a good reading on where to set each pass. For the plug gauge sometimes making a taper plug helps rather than a go no go. Mark the OD at your size. Helps with alignment to get it started in the bore and slides in until the right diameter. Also allows you to measure on your gauge where it did go into so you know how much more to take. Rather than just a no go gauge and guessing at how much more you have left.


----------



## Janderso (Aug 19, 2021)

Mitch Alsup said:


> Fitting a boring bar in a hole already less then 0.250" in size requires a really tiny boring bar.


With lots of flex!!


----------



## martik777 (Aug 20, 2021)

Janderso said:


> With lots of flex!!


Measured  about .002" with 1" length


----------

