I need to bore a hole to finish my X axis CNC stepper mount and I am confused as to how I attack this. I have a boring head and want to understand the proper way to utilize this. Do I need to bore an undersized hole with an end mill then slowly work the boring head out in diameter until it's the correct size, thereby making lots and lots of chips, or can I start with the boring head, about 0.01 under size and bore through then finish to the appropriate size, creating a slug of waste material removed from the center?
You will need a hole before you can use the boring head, they will not cut a hole in a solid piece of material.
Do you have a drill chuck or MT adaptor for your mill? (assuming that you will be using a mill to do this). Use the biggest drill you have that is about .02" to .03" undersized (or whatever you have that's undersized if you can't get that close). If you can't mount a large enough drill in your mill (don't know what you have for a mill so can't be specific) try drilling the part out in a pillar drill. Once you put the part back in the mill you will have to pick up your hole location from the part edges rather than the hole itself as a drilled hole is unlikely to be true enough to locate from.
You can then use the boring head to finish the bore to size taking at least a couple of cuts to get to the right size.
Then mark out a circle at the size you want and use the end mill to 'hog' out the material until it is .04"-.05" from the line (roughly 1 mm and easy to guess). It doesn't matter if the rough hole is round, oval or stepped as the first couple of cuts with the boring bar will make it true. I would start with straight lines and then using the handles on both the X and Y axis I would operate them in unison to 'guide' the cutter in a rough circle, keeping inside the line at all times. When you get close to the line replace the end mill with the boring bar and position it 'on centre' for the hole. Set the cutter so that it just rotates inside the hole without fouling and then bore out the remaining material using small cuts (especially at first). The first couple of cuts with the boring bar will probably be intermittent cutting so make sure you have the locks on all ways except the Z axis to stop the table 'jiggling' about as you bore.
What kind of material are you cutting, and what are you cutting it on?
Last week I was boring O-1 plate using a Bridgeport knock-off.
175-200 RPM .100"/side .006"/rev. Brazed carbide tool with Ø.75" shank and perhaps 3" extended out of the boring head.
Holes ranged from Ø.75" - Ø1.25" +0/-.001", 1.3" deep.
If I was running aluminium, I would be spinning the boring head as fast as the machine could take without going for a walk. Radial depth of cut as large as the cutting edge would accommodate. .006"/rev is max. autofeed (for roughing I wouldn't bother with the autofeed).
There is a fine line between investing the time in performing a process more efficiently, and just plain wasting time. Boring is just that, but for one hole it's not worth the thought.
Well, it could be worse. You could require a much larger hole and only have a 3/4 end mill. Fortunately, that is what boring heads are all about. Then you could also spend xx dollars to purchase larger drills whereas you could leave whatever amount you want to finish bore.
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======================================================= As indicated in previous replies you can't cut a slug of material with a standard boring head, however a special "drag cut" head and tool is manufactured that will do this.
Given the size of the hole and your equipment I suggest this is a good application for the infamous Silver & Demming drill set. Even with a
1/2 inch capacity chuck you can drill very large holes, just not in one pass. Most S&D sets come in 1/16 increments (for a reason), and if you step up the hole size by this amount and don't push things, that is keep the RPM and feed rate down and use plenty of high-quality cutting oil, you can drill out to 1-1/4 diameter (the largest one I have) with no problems. It should not be too much of a problem to go from 1-1/4 to 1.3??
In using the boring head remember there is a *LOT* of spring, so make several "dry" [cuts with no increase in the diameter setting] when you get close to size. You should do this until you get no cutting all the way through the hole. Use power feed if available. For good finish feed out as well as in, or retract the tool when withdrawing. It can be helpful to lap the face of your boring bar using fine grit wet-or-dry paper on a flat surface such as large HHS lathe tool or mill table. This will improve the surface finish of the hole. I use cutting oil or tap lube on the paper and wipe off with a paper towel. A few minutes with 600 grit should produce a near mirror finish.
A follow-on to my prior reply as a result of some off-list emails
A trepanning type boring head is shown at
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dont know how thick a material you can cut with this.
Another alternative if the depth of cut is 1 inch or less is a hole saw. [longer depth saws are available]
Note that these seem to cut quite a bit oversize from the indicated diameter. I have had good luck with these making tool holders for the KRF quick change tool holder system out of 1 inch thick CRS. I use a one inch hole saw and this gives me just enough to finish bore to
1-1/8. Run slow, back out and remove chips frequently, and use cutting oil. It can be helpful to drill one or two through holes [3/8 to 1/2) inside the 1-1/8 diameter but in the path of the saw blade. This will give the swarf some place to go. My biggest problem is getting the slug back out of the hole saw.
Nonsense. I've successfully done it with a Bridgeport, using a Bridgeport boring head and a hand ground tool. Granted, the cut wasn't real deep, only about 3/16", but something like 26 3½" diameter pieces were blanked out of a strip of stainless, alloy unknown, but in the 300 series, and certainly not
303. Key to success was the proper grind of the trepanning tool, plus the use of Boelube while cutting. Sulfur based oil didn't work.
That's what I was thinking. I made a huge pile of aluminum chips today with my rotary table and the Van Norman. Way faster than the same operation on my lathe.
I use the rotary table a LOT for making big holes and the setup is fast. Often times faster than using the lathe and a fixture plate.
Gunner
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politically feasible, and use that money to buy as many of the people's votes as possible'.
The rotary table method worked very well for me in boring out a transmission gear. Didn't have a boring head, and used a carbide end mill as the gear was seriously hardened. Came out real well.
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