Recommended spindle speed using a boring head on a Bridgeport

[ironwrx]

Hi. I’m not a trained machinist, but trying to learn as I go. I have a clamp bracket for a torque bar I am making for my Bridgeport Mill so I can use a newly acquired Tapmatic 50X tapping head. I loosely modeled my design after the stock bracket from Tapmatic’s owner’s guide. Mine, however is semi- circular to fit more snugly to the quill. I formed most of the bracket cold out of 3/8” x 1” flat bar using my Hossfeld bender. Then I drilled and tapped the clamp holes, and placed a couple of spacers in place to be able to bore the ID for a nice fit on the quill. The currant size is about 3-5/16”. I need to bore it to 3-3/8”. I haven’t had enough experience to know what would be a good speed to bore out this piece would be using a boring head on the BP. Here’s what I’m trying to to make, and what I have so far on my version. Any recommendations would be appreciated. Thanks, Jon

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[WobblyHand]

You are boring the clamp above to make it round? Or are you boring out the plate below it? What is the diameter? What cutter are you using HSS or carbide?

Generally speaking the formula for RPM is RPM = SFM / (D * pi/12 ), where D is the diameter of the cutter or boring diameter in inches, and SFM depends on the material and the cutter type. For mild steel use SFM = 90 if HSS, or 225 if carbide.

An easier to remember (approximate) formula is RPM = 4 * SFM / D

Big holes require slow speeds, sufficient motor torque, good clamping and a bit of patience.

 

[Jim F]

Easier to extend the arm on the tapping head.

 

[Smithdoor]

Hi. I’m not a trained machinist, but trying to learn as I go. I have a clamp bracket for a torque bar I am making for my Bridgeport Mill so I can use a newly acquired Tapmatic 50X tapping head. I loosely modeled my design after the stock bracket from Tapmatic’s owner’s guide. Mine, however is semi- circular to fit more snugly to the quill. I formed most of the bracket cold out of 3/8” x 1” flat bar using my Hossfeld bender. Then I drilled and tapped the clamp holes, and placed a couple of spacers in place to be able to bore the ID for a nice fit on the quill. I haven’t had enough experience to know what would be a good speed to bore out this piece would be using a boring head on the BP. Here’s what I’m trying to to make, and what I have so far on my version. Any recommendations would be appreciated. Thanks, Jon

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The photo is a tapping head.

Boring start low and work your up in rpms. There to many factors is the speed. If doing production it can calculated but takes time too and may need slow down

Dave

 

[ironwrx]

You are boring the clamp above to make it round? Or are you boring out the plate below it? What is the diameter? What cutter are you using HSS or carbide?

Generally speaking the formula for RPM is RPM = SFM / (D * pi/12 ), where D is the diameter of the cutter or boring diameter in inches, and SFM depends on the material and the cutter type. For mild steel use SFM = 90 if HSS, or 225 if carbide.

An easier to remember (approximate) formula is RPM = 4 * SFM / D

Big holes require slow speeds, sufficient motor torque, good clamping and a bit of patience.

I am boring the inside of the formed clamp. Currently 3-5/16” target = 3-3/8”


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[ironwrx]

Easier to extend the arm on the tapping head.

Yes, I’ve seen others do that, but Tapmatic recommends against that. I’m sure it’s easier, but I’ve come this far…, so why not.


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[ironwrx]

The photo is a tapping head.

Boring start low and work your up in rpms. There to many factors is the speed. If doing production it can calculated but takes time too and may need slow down

Dave

Yes, I understand that the photo is a tapping head. I included that to show what I am making.


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[WobblyHand]

I am boring the inside of the formed clamp. Currently 3-5/16” target = 3-3/8”


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For HSS boring bar, and 3.375" diameter, I come up with about 100 RPM. What ever you do, start slow, (much less than 100) and listen to the mill. If you hear vibration or experience chatter, slow down.

 

[Jim F]

Yes, I’ve seen others do that, but Tapmatic recommends against that. I’m sure it’s easier, but I’ve come this far…, so why not.


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Tapmatics at work have a long rod on them, so.............

 

[MrWhoopee]

Just got a 50X, used a 5/16 rod in the eye cast into the right side of head.