What's the Proper Tool To Do This on a Bridgeport?

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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Natchamp
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What's the Proper Tool To Do This on a Bridgeport?

Post by Natchamp »

Sorry if this sounds like a stupid question, but here it goes. I am trying to plan out the best way to precision bore a whole that has a square shoulder on the bottom with my Bridgeport mill. My mill has a MT#2 spindle. I have attached a jpg of what I am referring to. I had originally thought that I would use a boring head like this:

Boring Head

However, the smallest ones I've seen is 2". The hole, which is for a bearing, is 1.850". One of the important things, other than a precise bore, is to have a square shoulder for the bearing. Please tell me what I don't know! Thanks.

Mark
curley

Re: What's the Proper Tool To Do This?

Post by curley »

Natchamp, the boring head has holes in line with the spindle axis and will bore a hole as small as your bars will allow.
Regards, Curley
Dave_V
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Re: What's the Proper Tool To Do This?

Post by Dave_V »

Mark,

The physical diameter of the boring head has little bearing on the minimum diameter of the hole that you can bore. The main consideration is that of the # 2 morse mounting. I wouldn't place anything larger than a 2" boring head on a #2 shank.
The sketch indicates that the depth of the hole is well within the range of a 1/2" shank boring bar. It is the size and length of the bar and HOW it is held in the boring head that matters. There are more than one positions in which to place the boring bar. A set of bars will have a selection of sizes and lengths of bars to choose. Use the shortest and heaviest bar that will do the job. The finished diameter, as well as the amount of stock to remove, will dictate how you setup the boring head ( which hole the bar will be held in ).

Dave
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Harold_V
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Re: What's the Proper Tool To Do This?

Post by Harold_V »

Mark,
First, you may be confusing the size of a boring head with the head's ability to bore a specific sized hole. There's generally no relationship. A 2" boring head is capable of boring a 6" hole when tooled properly, and a 4" head is likewise capable of boring a very small hole when appropriately tooled. Most boring heads will accommodate a bar out the side of the head to bore large holes, and there's adapters to hold miniature bars for the larger heads. Travel of the head is what limits you when you get smaller heads. Rigidity of small heads is also questionable, so you really need more than one sized head if you're serious about boring. If you plan to buy just one, I think I'd recommend a larger one rather than a smaller one.

To bore a hole with a square shoulder is a tough order unless you have a facing boring head. They're quite expensive and not all shops have them. That's no reason to not do your job as you'd like, though.

While you can achieve acceptable results the way you've drawn the attached pic, a bearing should bear only on the outer race. You would be wise to bore your hole slightly deeper (perhaps about .005") except for the outer race area, which would then locate the bearing properly. The shoulder you need is a narrow enough that you can do it by a straight faced boring tool, running it very slowly to achieve a nice clean cut without chatter after you've established the proper diameter. What I'd do is back off the bar a few thou and then go for proper depth, having already bored to within perhaps a couple thou originally. If you try to get to depth on each pass you're likely to have steps and risk screwing up the bore as well. The final cut can even be done by hand powering the boring head if you find you're having trouble with chatter. It takes only a minute or so to achieve a nice clean shoulder as long as you're not cutting with the full face of the tool.

Bearings should not come close to making contact anywhere except for the outer race. If the inner race makes contact with the shoulder, I'm sure you can see that's not a good thing.

Does this make sense to you? If I have you confused, ask and I'll restate the procedure.

Harold
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philinmt
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Re: What's the Proper Tool To Do This?

Post by philinmt »

The other post are right on, use your quill stop for the bottom of the hole. set it .01 deeper than you want until you are .200 from the finshs size then reset it to your finsh depth, that way you will not hit bottom and chatter or brake the tool...Phil in Mt
Natchamp
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Re: What's the Proper Tool To Do This?

Post by Natchamp »

Thanks to all. What I didn't know was that the boring bars cab also be held in the boring head vertically (same axis as the spindle). I pictured them mounting horizontal. Now I understand you can mount them both ways. Also, thanks for the machining and clearance tips. This list is really incredible and the comardity (?) of people all too rare. I hope I can answer more questions than I ask.....some day. cheers.
Mark
Hanz
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Re: Boring Heads

Post by Hanz »

Before you bid on that auction, check prices! That auction is only for the head, plus $27.50 for R8 spindle adapter and shipping. I just bought a 3" head w/R8 adapter, PLUS a 12 pc 3/4 " shank carbide boring bar set from Enco, for $99! AND I did my duty to help with feeding the hungry overseas!
[url=http://www.hanzenginehouse.com]www.hanzenginehouse.com[/url]
Natchamp
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Re: Boring Heads

Post by Natchamp »

Thanks Hanz. I just used that for illistration. Side note, don't you do engine work? You might check out my website and see what my previous project was, you'll get a kick out of it.

Mark
THE BEAST
Bob_W
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Re: What's the Proper Tool To Do This?

Post by Bob_W »

Didn't see it mentioned above, but one option would be to bore the hole on a lathe. From the sketch it seems like it would be within the size limits of a small lathe if you have one available. Do you have to use the mill?

Bob W
Natchamp
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Re: What's the Proper Tool To Do This?

Post by Natchamp »

Bob, I don't have a lathe yet. I hope to get one shortly but have other things to get first (like my cnc mill running!) Thanks.
Mark
Hanz
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Re: Website

Post by Hanz »

Nice work, Mark! I looked at all of your projects. How did the V8 914 run and drive? Very nice website also. I like consistant multiple frame pages. I am working on my little ol' site and will post it soon. Take care.
[url=http://www.hanzenginehouse.com]www.hanzenginehouse.com[/url]
Anonymous

Re: What's the Proper Tool To Do This?

Post by Anonymous »

If you have a rotary table finish the bottom out using the rotary table and an endmill. Bore your hole to size and depth. Set it up on the rotary table, indicate it in center, then finish mill the bottom.

Kevin
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