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Sportandmiah
04-21-2010, 11:58 AM
From a previous thread, http://bbs.homeshopmachinist.net/showthread.php?t=39871 , I found a boring bar. It's from Harvey Tool, 1/4 round shank, OAL 2", min bore diam of .240, and max bore length of 1", all carbide. I now have to make a boring bar holder for my Sherline as they only sell ones for 3/8 shanks. Here of a few of my questions, as I've never made a round boring bar holder before:

http://i160.photobucket.com/albums/t182/bigsport/29000_boring_bar_pic.jpg

1. What size hole should I use for the actual bar to fit into? Does it have to be a super accurate fit?

2. How high should said hole be from the base of the table? The bar has to be on center if I remember correctly. I plan to mount a dead center in the spindle and measure from there.

3. Does anyone have any good literature online in regards to using the boring bar correctly? My last project of wheels turned out decent, but I felt as though I wan't using the bar correctly or possibly not mounted correctly.

4. I plan on using some hard steel chunks I have sitting around for the holder...would aluminum work also for the holder or would that be too soft?


As always, pictures really help as I have trouble computing text into pictures sometimes! ;)
Any help would be appreciated. :)

hornluv
04-21-2010, 12:26 PM
Why don't you just hold the stock for the holder in your tool post, indicate it in so you know it's nice and straight, and then drill and ream the hole in place. Then you know it's on center. I would go for a relatively tight slip fit where it slides in but there's no discernible slop side to side. Try .250, but if that doesn't fit, have a .251 reamer handy.

With regards to how to use it correctly, boring bars flex so you want to take depths of cut that are consistent so you know how it will behave. I like to rough in to about .020" under size and then take several passes of .005 with a measurement in between each to make sure I know how much it is really taking off. This gives you much more predictable results than if you take heavy cuts and leave one light pass for finishing.

Arthur.Marks
04-21-2010, 01:04 PM
The quick and easy method is to just get a bushing for your 3/8" holder that reduces it to 1/4". Then your holder can effectively use both sizes. For example, McMaster catalog page 2599: in the 5-10$ range.

As far as the necessity of precision for the hole you mount the boring bar in, I would say it is nothing to worry about. What you need to make sure repeats is the perpendicularity of the movement the bar makes---not the mount. If your mount is off, it will just affect how the tool is presented to the workpiece. In other words, your lead angle, etc. If you set everything up and your hole is off perpendicular by a few thousands or so, it really makes almost no difference to geometry at the point of cut. What matters is the movement of the whole tool + holder to the workpiece. If that is off, you will get a tapered bore no matter how well aligned the first two are.

Quickest and easiest, IMO, is to make your own bushing for the Sherline holder. Make sure you slit it so the bushing can clamp your tool shank when tightened.

Sportandmiah
04-21-2010, 01:06 PM
Excellent advice on centering the hole, thanks!
In regards on how to properly use the boring bar, what confuses me at the angle it must be setup. Because it is round, it can move. How should the front of the cutter look, or be angled. Pictures appreciated.

snowman
04-21-2010, 01:13 PM
I might have a small boring bar in 3/8 that I can send you cheap.

I just bought about 20 lbs of HSS boring bars. I'm going to pick through what I need and post the remainder on PM or Ebay.

Arthur.Marks
04-21-2010, 01:23 PM
...what confuses me at the angle it must be setup. Because it is round, it can move. How should the front of the cutter look, or be angled. Pictures appreciated.

A great thread on that (with pictures!:) ) here: http://bbs.homeshopmachinist.net/showthread.php?t=40758

hornluv
04-21-2010, 01:26 PM
The front of the bar should look flat. You don't want it pointing down, since that would make the rake angle negative, but if it is angled upwards too much then it will decrease the relief angle to the point that the tool is rubbing more than cutting.

Arthur.Marks
04-21-2010, 01:30 PM
I like to rough in to about .020" under size and then take several passes of .005 with a measurement in between each to make sure I know how much it is really taking off.

In my experience, this method will only work with HSS. Carbide you need a sufficient depth of cut or it is unpredictable. Depth of cut depends on the radius of the tool and how sharp it is. Minimum cut on a new tool is the nose radius. For example, a tool with a nose radius of 1/64" will need a .015" DOC to work reliably and achieve a good surface finish.

Care to chime in on that, hornluv, as the OP has a solid carbide tool... Do you mostly use HSS with your method?

hornluv
04-21-2010, 02:26 PM
Yes, I use HSS and missed the part about the carbide. I like your rule of thumb about the nose radius. I'll have to store that one away in my brain. Thanks.

MTNGUN
04-21-2010, 02:49 PM
In my experience, this method will only work with HSS. Carbide you need a sufficient depth of cut or it is unpredictable. Depth of cut depends on the radius of the tool and how sharp it is. Minimum cut on a new tool is the nose radius. For example, a tool with a nose radius of 1/64" will need a .015" DOC to work reliably and achieve a good surface finish.
Agreed, concerning radiused tools.

However, the solid carbide boring bars usually have a sharp leading edge, similar to a HSS bit. I routinely use them to shave a tenth or two at a time.

Some of my small boring bars are clamped directly in the tool holder. Others are clamped in a sleeve so that the bar can extend further from the tool holder. Pic shows one of each.
http://i487.photobucket.com/albums/rr235/mountainmolds/boring1.jpg

Front view.
http://i487.photobucket.com/albums/rr235/mountainmolds/boring2.jpg

Note that you'll want the type of tool holder that has the little V-groove at the bottom.

Black_Moons
04-21-2010, 03:00 PM
As for the DIY aspect:

Generaly do not use aluminum for toolholders, it much more flexable.
Use mild steel, thats right, boring mild steel, its just as rigid as the highest end hardened steels oddly enough, and you'll need enough metal for rigidity such that strength is not a consern at all, so mild steel is fine.

Arthur.Marks
04-21-2010, 03:02 PM
However, the solid carbide boring bars usually have a sharp leading edge, similar to a HSS bit.
I didn't realize that. Thanks for the correction :)

allthumbs9
04-21-2010, 03:11 PM
Sportandmiah,
Here is a picture of the boring bar holder I made for my Sherline lathe. It's just a block of aluminum squared up, then drilled for the mounting bolts, copying the geometry of the Sherline holders. Then I secured it to the cross slide, put a ctr drill, then drill in the headstock chuck to drill the hole for the bar in the block, on center. It has worked great.http://i689.photobucket.com/albums/vv251/majimicromachineshop/SIMG0007_2.jpg

dockrat
04-21-2010, 04:40 PM
Here is a pic of a double barreled boring bar holder I made for my 10x28. I milled a block of mild steel to fit my toolholder then drilled it out on centers with the drill in the chuck. one hole for 1/2" and the other for 3/8". When in use, I put a flush mounted blank in the unused hole just to keep the swarf out.

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1066Medium.jpg

reggie_obe
04-21-2010, 04:40 PM
Or you could skip the quick change toolholder and make a dedicated holder like this: http://cgi.ebay.com/Armstrong-South-Bend-Boring-Bar-Holder-Toolpost-0-BB-/200461218082?cmd=ViewItem&pt=BI_Tool_Work_Holding&hash=item2eac6b7122
Rigidity is key in both the holder and the boring bar itself to produce accurate work. If your cross slide had a rear "T" slot, you might consider making a holder that fits there.

Boucher
04-21-2010, 06:00 PM
Allthumbs9 has outlined the basic concept of using a drill held in the headstock to drill the hole in the tool holder held on the cross slide. The choice of materials is not a big deal. Steel would be better but aluminum will work for this size machine. Round bar is easier to work with. Face the bottom end so it is square to the axis and flat. This is a project shown in one of the Lathe Videos by Rudy Kouhoupt and produced by this sites sponsorer HSM. As a newby it was one of my first projects and I still use it. I now have a quick change tool post and tend to use it more. The original one is there and works just as good. You might consider making several for different size boring bars. They can be adapted down size by using bushings but a correct size holder is better.