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Boring Head How to Question

adh2000

Titanium
Joined
Dec 21, 2005
Location
Waukesha, WI
Criterion boring head in a mill, happens to be a Deckel FP1. Boring 2” diameter through hole 4” long. Complication is that the first half inch is 2”, then the bore expands to 2.030” for 3”, then the last half inch is back at 2”. So how to do this. How do I extend the boring bar while I’m in the bore? I think a boring and facing head might do this, but I don’t have one of those.


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is the 2.030 dia for clearance? What tolerance, does it need to be bored, or are just the 2.000 dias close tolerance?

If the 2.030 is clearance, I would do that with a necked em, then bore the 2.000 dias.

Otherwise, you'll need to do the 2.030 by feeding down off center, then feeding over to cl, then down.
 
Do you have a rotary table?

If so, you could first center the workpiece bore on the table axis, the adjust the RT-and-workpiece-assembly is coaxial with the spindle to bore through to 1.980 inch or so diameter.

Once that's done, reset the spindle to place the top edge of the boring cutter a half inch into the hole, turn on the spindle, move the machine table 0.015 inch laterally, and feed along the bore slowly while rotating the rotary table.

Finally, return the rotary table and workpiece to coaxiality with the machine spindle to finish the 2 inch diameters.

Yes, it's a clumsy way to do the job . . . but it can work.
 
Bore your 2-inch diameter to finish. Then position the tip of your boring bar in the correct spot to start your 2.03. Put your machine in neutral so you can turn the spindle by hand. Adjust the head out a few thou and turn the spindle until the bar is mostly free. Rinse and repeat until you are at your 2.03 dimension. Then put the spindle in gear and bore to proper depth. You may need to rework the clearance on your cutter so the heel doesn't wipe out the 2.000 bore as you feed the cutter into the bore. If the transition dimenson is critical, start towards the middle and finish the bottom dimension. Then switch to a back bore boring tool and finish the top dimension.
 
Not sure what your part looks like, but if it would fit in a lathe it seems like it'd be more straightforward

Edit: I'm sure that's obvious to the OP, given his post count. But may not be obvious to all readers

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is the 2.030 dia for clearance? What tolerance, does it need to be bored, or are just the 2.000 dias close tolerance?

If the 2.030 is clearance, I would do that with a necked em, then bore the 2.000 dias.

Otherwise, you'll need to do the 2.030 by feeding down off center, then feeding over to cl, then down.

Yes. Don’t see how a necked em would do it unless I was on a rotary table, which I’m not.


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Not sure what your part looks like, but if it would fit in a lathe it seems like it'd be more straightforward

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That’s for sure. It’s a cross bore in a 20” long casting so would take a big lathe and some fixturing headache.


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Bore your 2-inch diameter to finish. Then position the tip of your boring bar in the correct spot to start your 2.03. Put your machine in neutral so you can turn the spindle by hand. Adjust the head out a few thou and turn the spindle until the bar is mostly free. Rinse and repeat until you are at your 2.03 dimension. Then put the spindle in gear and bore to proper depth. You may need to rework the clearance on your cutter so the heel doesn't wipe out the 2.000 bore as you feed the cutter into the bore. If the transition dimenson is critical, start towards the middle and finish the bottom dimension. Then switch to a back bore boring tool and finish the top dimension.

I’m kinda liking this idea. Thanks. I think it’s doable.


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I like the bore to 2" all the way then switch. Could you do something with an internal grinder to open up the bore enough to swing the boring head. Maybe mount the grinder to the boring head for ajustability. I have seen photos of home shop types mounting a Dremel to the lathe toolpost for internal and external grinding.
Bil lD
 
Yes. Don’t see how a necked em would do it unless I was on a rotary table, which I’m not.


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I didn't notice it's a manual machine at first. How good are you at drawing circles on an etch-a-sketch? I think Gbent's idea is the only one that's going to work for you.
 
Bore your 2-inch diameter to finish. Then position the tip of your boring bar in the correct spot to start your 2.03. Put your machine in neutral so you can turn the spindle by hand. Adjust the head out a few thou and turn the spindle until the bar is mostly free. Rinse and repeat until you are at your 2.03 dimension. Then put the spindle in gear and bore to proper depth. You may need to rework the clearance on your cutter so the heel doesn't wipe out the 2.000 bore as you feed the cutter into the bore. If the transition dimenson is critical, start towards the middle and finish the bottom dimension. Then switch to a back bore boring tool and finish the top dimension.

Tried this out. Tedious and time consuming but result is fantastic. Did I mention it was time consuming? Also it took a long time. Thanks for the suggestion.
 
I might try a variation on gbent’s method.

After boring through at 2.000”, position the spindle so the cutter is in the section you wish larger, start the mill, crank the table .015” to the right, and bore a short distance. Back the quill up to your starting point, then repeat but first crank the table back to center, then continue .015” to the left.

Do it twice more, but this time cranking the saddle in and out.

You”ll end up with a cloverleaf rather than a round bore in the central part. Within that cloverleaf, you can easily adjust your boring head to cut larger, and feed the full length of the center section.
 
I think Gbent's idea is the only one that's going to work for you.

That... or he begs, buys, borrows or rents a boring and surfacing head of the Chandler-Duplex and competitors tribes.

Non-trivial investment if yah near-as-dammit never NEED such, but some might argue that with infrequent use, it is all the more the only kind worth having at all.
 
Bore your 2-inch diameter to finish. Then position the tip of your boring bar in the correct spot to start your 2.03. Put your machine in neutral so you can turn the spindle by hand. Adjust the head out a few thou and turn the spindle until the bar is mostly free. Rinse and repeat until you are at your 2.03 dimension. Then put the spindle in gear and bore to proper depth. You may need to rework the clearance on your cutter so the heel doesn't wipe out the 2.000 bore as you feed the cutter into the bore. If the transition dimenson is critical, start towards the middle and finish the bottom dimension. Then switch to a back bore boring tool and finish the top dimension.

BTDT many times back in the day, .and it's not that time consuming because you can put 0.005'' DOC on at a time and rotate under power - because the boring bar flexes enough to allow you, …..& 3 X 0.005 = 0.015 on rad, which = 0.030 on dia = job done :)
 
I might try a variation on gbent’s method.

After boring through at 2.000”, position the spindle so the cutter is in the section you wish larger, start the mill, crank the table .015” to the right, and bore a short distance. Back the quill up to your starting point, then repeat but first crank the table back to center, then continue .015” to the left.

Do it twice more, but this time cranking the saddle in and out.

You”ll end up with a cloverleaf rather than a round bore in the central part. Within that cloverleaf, you can easily adjust your boring head to cut larger, and feed the full length of the center section.

This is exactly how I've always done it on manual machines without a facing type attachment or rotary table. Works a treat.
 








 
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