Need Help!- Boring Question

[nfrees114]

Hey All- So I am boring a 5.625 hole in a piece of 1018 Steel tubing (3/8"wall) that's been welded into a piece of 4x8x3/8 rectangular tubing that's been distorted. I am using a boring bar but cannot seem to get the chatter to stop and leave a nice finish. I was thinking about using a face mill (picture attached) that i have and was wondering if anyone has ever done that and if it works well. also if not i was wondering if anyone could help with maybe some speeds and feeds of the boring bar that would maybe help with me getting a good finish. the s&f that i'm using now with the boring bar is about 350rpm and about 1ipm with a .050" depth of cut (diametral depth of cut .025 per side). any help would be greatly appreciated. thanks guys!!
-Nate

[vigilante212]

it will prob still vibrate with the endmill. You prob need a more rigid setup for your workpiece.

[Geof]

The facemill will probably be worse.

You do not mention depths or anything but I am guessing the tube you are boring is just sticking up from the rectangular tube which is clamped down onto the table. This gives the opportunity for a lot of flexing both in the walls of the tube being bored and in the face of the rectangular to which it is welded. It is also almost certain you are using an insert cutter which is negative rake and these cutters exert a lot of force against the surface being cut increasing the flexing. And to compound the problem the flexing can be greater in different directions around the tube depending on whether it is directed across the reactangular tube or along the rectangular tube. The result is every rotation of the cutter make the tube flex and return and vibration builds up.

What to do?

You need to stabilize the tube being bored and one way to do this is make a wooden collar cut to fit the tube with a bit of stiff foam rubber between. Make tis collar out of pieces large enough to extend beyond the ractangular tube, clamp it on and then put packing pieces between it and the table at either end and clamp them down. The reason to use would is that it absorbs and vibration that does develop, the foam rubber helps with this, and wood is not straong enough or stiff enough to move your workpiece out of position when the collar is clamped down.

A quicker method which may not be feasible because of your tube size, is to wrap strips of lead around the tube and overlay them with electrician's tape tightly wound on; lead solder works great for this. But for your size you would need many feet.

[packrat]

Not knowing what type of machine or boring bar is a problem with diagnosis.
so I'll guess using what I have to use, a Bridgeport and adjustable boring head.

Your spindle speed is too fast for the diameter your cutting. Some where around 150RPM would be better. On the feed I would use .0015 per revolution setting(remember Bridgeport.)

A HSS bit will cut better than the carbide , they can be sharper and cause less spring back at the actual cutting surface. Thats usually what causes the chatter. Use the least amount of tool length that you can.

[billystein]

i must go with packrat on this one. you need to slow the r's down until the chatter stops. i
would use solid carbide boring bar also.
good luck

[billystein]

i would agree with packrat about the r's. keep slowing it down until the chatter stops. i would use a solid carbide bar to help reduce the chatter.
good luck

[sambo67]

what is your tool's NR.1018 likes a bigger NR .

[Cruiser]

Ditto on Speed ! also, depth of cut in relation to extension of bar is critical. The extention to bar diameter ratio, and even more so is the geometry of the tool used to make cut. If the tool is healing at all it will push tool away from cut and chatter. If too much positive it can gouge and chatter. If too much negative it can load and chatter. Best bet is to back off on depth of cut and gently whittle away. Also take a magnifying glass to tool point and look for any tattle tales as to what is going on.