Next Project Boring Head

mickri

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Now that I am done with the ER32 collet chuck it is time to think about my next project. A boring head. In the not too distant future I will need to turn some tapers. A boring head in the tailstock would provide the necessary offset so I could turn the tapers between centers. I have been looking at DIY plans online. The attached plans are representative of what I have found. One is your typical round boring head. The other is a rectangle. I have stock on hand that I could use to make either one. I also found this thread on making a rectangular boring head. https://www.hobby-machinist.com/threads/shop-made-boring-head-project.22120/. I found this thread very interesting because he used an end mill to cut the dove tails. I don't have a dove tail cutter and would have to buy one. I was reading a website about making a boring head where it was stated that dove tail cutters are easily damaged. No experience with dove tail cutters but I have damaged end mills making the tool holders for my Norman style tool post.
All of the boring heads that I have seen use dove tails. Is there a reason for this? Why I ask is that I have a key way cutter and could make a T slot instead of a dove tail. Here is a rough sketch of the body. Seems to me that this would be easier to make than dove tails. If you guys think this has merit I will do a detailed sketch. Because it seems to take me forever to get something done I should get started on this sooner the better.

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macardoso

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I think the advantage of the dovetail is that either using a tapered gib, or more commonly on boring heads a split dovetail with adjustment screw, you can take out all the slop without an extremely high level of accuracy in the machining. The dovetail has a single adjustment that takes out play in the axial and radial directions, while a T slot would need two. That being said, I don't see any reason you couldn't make a boring head this way.
 

benmychree

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If you observe cutting speed and feed limitations, there is no reason to fear using a dovetail cutter.
 

Chipper5783

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Making a dovetail cutter, based on a triangular insert is a very doable home project. I did. I found that it cut slowly (a single tooth cutter banging away) - but the result was great. My application was the DTs on Aloris style QCTP holders.
 

Norseman C.B.

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I made the one in the 2nd PDF file you show recently, it's not a real difficult project and works very well....
The first one you show looks like another project for me down the road............:grin:
 

mickri

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I am going with the rectangular boring head shown in the 2nd PDF. I cut two 2 1/4" long pieces off of a chunk of 2" x 1 1/4" 1018 steel this afternoon. It's a start. Probably won't get back to it until next week. Have other projects on my plate that will take up the rest of the week.
 

mickri

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If I decide to use a dovetail cutter instead of an end mill to cut the dovetail what size dovetail cutter should I buy?
 

mickri

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Had some time today and was able to true up the ends of the pieces that I had cut with my trusty hacksaw. I also like to make a 3D drawing. I use google sketchup and have found that doing the drawing gives me a good idea of the order of the steps I will have to take to make something. Here's my drawing of the two main parts.

291281
 

mickri

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Two things that I am wondering about. One is what size boring bars should I drill the holes in the head for? I don't have any metric drills and my imperial drills are in 1/64 increments. I am leaning towards 1/2" boring bars. Other choices under consideration are 3/8, 10 mm & 12 mm.

The other thing is the piece that the lead screw screws into. Several questions here. First is how precisely does this piece have to fit in the slot. The plan that I am loosely following has a .60 wide slot with a .46 wide piece. This leaves .007 clearance on each side. That would be a sloppy fit imho. The piece in the plan is rectangular being .46 wide by .62 long. With the sloppy fit I don't think that it provides much if any guidance as the boring head moves back and forth. In looking online I have also seen this piece being round. In the thread I referenced in my first post this piece is also round. A round piece would be the easiest for me to make.

I want the shank to be round. I have an ER32 collet chuck that lives in my mill/drill. I also have an ER32 collet chuck with a mt2 taper that pretty much lives in the tailstock on the lathe and an ER32 collet chuck for the lathe spindle. With a round shank the boring head is usable in any of the ER32 collet chucks.

With a round shank and a round piece for the lead screw I could make the shank long enough to extend through the base to serve both as the shank and for the lead screw.

boring head plan 2 with shank.jpg

Then the question becomes how to attach the shank to the base. My initial thought was to drill and tap a hole or two through the base and the shank for a bolt or machine screw. I have also thought of using roll pins. My concern is sheering off the bolt or roll pin when using the boring head in the mill. The shank would be 1/2" with probably 1/4" bolts or roll pins. The plan uses four 1/4x20 screws to attach the shank to the base. Would this work?
 

bill70j

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Two things that I am wondering about. One is what size boring bars should I drill the holes in the head for? I don't have any metric drills and my imperial drills are in 1/64 increments. I am leaning towards 1/2" boring bars. Other choices under consideration are 3/8, 10 mm & 12 mm.
You might consider making your boring bar holes as large as is feasible, which gives you the flexibility to sleeve for smaller diameter bars. The boring head I use has 1/2" holes, and so far I have made sleeves for 1/4", 6mm, 7mm, 8mm, and 10mm boring (and threading) bars.
 

mickri

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That sounds like a good suggestion. Right now I have the holes at 1/2." I could go maybe as large a 3/4." Is it important for any reason to have the inner hole centered in the head?
 

Norseman C.B.

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The only changes I made to the original plan were reducing the drive shank to 3/4"
and using a piece of round bronze for the adjusting nut instead of a small steel rectangle, also went to 1/2" boring bar holes instead of 3/8".
The plan is solid for use as written keeping it centered is crucial to me for adjustment YMMV ...........................:cool:
 

mickri

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Need some help. I have never used a dovetail cutter. Don't own one and have never even seen one except in pictures. They are not expensive but not cheap either. I am thinking about buying a couple. My problem is what size do I need to buy to cut a 60 degree dovetail that is 3/8" high and goes in around 3/16." I have searched the web for the sizes of dovetail cutters. Based on what I found I would need a 1" dovetail. That seems pretty big to me. Are these made to standard dimensions? Or is every manufacturer different? Help me out.
 

bill70j

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Mickri:

I bought a 60deg X 25mm HSS dovetail cutter from Banggood for $9.99 to cut dovetails for some AXA tool holders. It worked great and is still sharp.

I have had good experience with Bangood's Chinese HSS dovetail cutters, as well as with their carbide end mills. Here is the selection of dovetail cutters they offer, including a table with specific dimensions. You can see from their sizing chart that the 25mm cutter will cut a dovetail 10mm deep, which is just over the 3/8" that you need.

Unfortunately, you will need a way to hold these cutters, all of which are metric. Since I have a number of their carbide end mills as well as their dovertail cutters, I invested in a set of metric R-8 collets to hold them.

HTH, Bill
 
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mickri

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I use metric ER32 collets in the mill/drill so metric isn't a problem. And 25mm is basically a 1" cutter which is what I had found as the size I needed in my research. Thanks for the use report.
 

Cadillac

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I’m not seeing how you’ll adjust the head. The head of screw is usually cut into top and bottom pieces then the head is grooved to interlock with I believe top portion. Bottom has a ear on it to engage the screw so it has two flat surfaces. Or flip flopped. Just a thought.
 

mickri

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If you look at the plan (boring head 02 posted above) that I am loosely following the lead screw is trapped against the head by a small plate. I am debating whether to do that or to put a nyloc nut on the lead screw at the other end of the head. One way or another I will do something that holds the lead screw in place as you turn it.
 

mickri

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Life has been busy but it looks like I will get some shop time next week to finish this project. My indecision at this point concerns what size boring bars should I use. The choices seem to be either 3/8" or 1/2." If I drill for 3/8 I can always increase it to 1/2" but can't easily go backwards from 1/2 to 3/8. I have never used a boring head and have no clue which size is better or if it makes any difference. Another question. I have seen boring heads that besides having two holes in the top also have a hole in the end for a boring bar. See my drawing in post #9 above. Is this a good thing to have or not?
 

mmcmdl

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I would go .500 and put that bore in the end also . Most heads are .750 bores . If you need to use smaller bars , use a split sleeve on them .
 

mikey

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Let me offer some food for thought, although the choice of boring bar is up to you. You have an Excel Mill Drill, which is a benchtop mill similar to an RF-30, correct? I would consider the forces the head generates as part of your decision tree.

The boring bars in a boring head encounter the same three forces they do on the lathe - axial, tangential and radial forces. However, the MILL experiences an additional force - Centripetal Force. This is a real force that is sustained by the mill, which is why a bigger mill with bigger mass that can go slow enough can bore bigger holes. Not to get too technical here but it will help you think this through. The formula for Centripetal Force is:

Centripetal force = mv2/r, where m = the offset center of mass from the spin axis, v = rotational speed and r = radius of the tool holder/tool assembly. The forum software won't allow exponents so note that this is MV(squared) / R. Things to note:
  • M is your boring bar. The bigger and/or heavier the bar is, the bigger the CF becomes.
  • V is your rotational speed. The faster you go, the greater the CF becomes ... very quickly.
  • R is the extension of the bar out from the spindle centerline. Note that as R increases, CF actually decreases. What this means is that as your required hole gets bigger, CF gets smaller IF you can go slow enough.
  • When CF reaches a certain point it will begin to cause the mill to move or vibrate. This varies with the mill, speed, size of the boring bars, how much extension you have on the boring head, type of boring bar you're using (HSS, cobalt, brazed carbide or inserted carbide). If you use a big enough bar and go fast enough, the CF can get big enough to make the mill literally walk across the shop and down your driveway. This is also why a bigger, heavy mill can bore bigger holes - it has the mass to resist the CF the head generates. Got it?
With the above in mind, and remembering we are speaking of a benchtop mill, smaller bars are probably a good idea. You might think that there is little difference between the weight of 3/8" and 1/2" bars but there is where CF is concerned. Using sleeves with smaller bars also adds to the mass. I suspect your mill can handle 1/2" bars if you bore out to maybe a max of 3" or so. Beyond that and the mill may start to vibrate if you cannot go slow enough.

I have multiple boring heads that take either 3/8" or 1/2" bars and whenever I can, I use the head with the smaller bars and this is especially true when the bore diameter goes up. This allows me to go faster for a better finish without the mill moving much at all. On smaller bores, the size of the bar becomes less important.

As for the side hole, I suggest you incorporate it if you can, not just because it allows you to put a boring bar there to bore bigger holes but also because you can put a shaft in there that holds adjustable weights to counter CF. We'll talk more about this after I build one.

In any case, think about it before you drill holes.
 

Titanium Knurler

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Wow, I learn something every time I tune-in to H-M! Centripetal force increasing with an increase of mass and velocity of the boring bar makes sense but a decrease with an increased radius is a bit counterintuitive, at least for me. So it seems to me that when using the same size boring bar that with an increase of the hole diameter you are boring, the centripetal force decreases for a couple of reasons: the first reason is as r, the denominator, increases CF will decrease according to the formula for CF, the second reason is that if you maintain a constant SFM cutting speed you will decrease the velocity(v), one of the numerators, which will also decreases CF.

Small bars, slow speeds, big holes decrease vibration(CF). Good to know, thanks Mikey.

However, I just remembered that the original post is to make a boring head to be used in the tailstock to achieve a taper and will not be rotating so in this case I would think the bigger the boring bar the better.
 

mickri

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Mikey, Thanks for the info. I like that kind of info because it helps me understand how things work. My mill/drill is the next size up from the RF 30. The slowest speed is 90 rpm. Using my mill/drill has been a real eye opener on the forces involved.

While the initial projects that I will use the boring head for are turning some tapers on the lathe down the road it will also get used for boring holes.

The idea to use counterweights is interesting. On my boring head the holes for the clamping screws are drilled and tapped all the way through. I did this so that I could attach a flat bar or angle iron that would extend out over the ways of my lathe and have adjustment screws to keep the boring head level when turning tapers. I could use those same holes to attach counterweights to the boring head. Something to think about.

I think that I will start out with 3/8 holes. I can always increase the size to 1/2 if I feel the need for that down the road. I could also make another head with 1/2 holes.

Again thanks for the help with this.
 

Titanium Knurler

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mickri, looks like a neat project you are working on and I wouldn’t want to discourage you from it but have you looked at a tailstock offset device like the ones pictured below? The Royal I bought used on eBay. It is nice because the center has a ball nose and there is a spirit level to help you position it since, as you know, the offset will change if the offset device tilts. The second photo is an inexpensive offset device that is easily found new online. They are of course only designed for forming a taper on a lathe so would not help you with your boring needs on the milling machine. Great project; keep us updated! TK

67C3FAA0-F51D-469E-AAB0-3EBA2B2C546A.jpeg

8F0F2DC0-84D4-4BAE-92F6-743A56D62CF5.jpeg
 

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mikey

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I really didn't mean to go into boring on the mill here. I simply wanted you to know how to think about your tooling because I guarantee you that one day your mill will begin to move when boring a hole. Since the mass of the bar is fixed and your extension is also fixed by the size of the required bore, the only answer is to alter speed. Since CF varies with the square of velocity, even a tiny bit of speed reduction will often resolve the issue. This is made easier if you have variable speed control. Then the only worry is if this reduction in speed will adversely affect the finish requirements you have.

Related to speed is the type of bar you use. Inserted carbide is a common choice in hobby shops but that type of bar requires higher speeds to produce good finishes. Faster speeds lead to higher CF. This is why I prefer cobalt or solid carbide boring bars on the mill - better finishes and it is easier to hit your required size because you aren't dealing with a nose radius.

Anyway, lots to think about.
 

jwmelvin

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Of course, that relationship above is in terms of linear velocity. If one considers angular velocity, centripetal force is m*r*ω^2, where ω is angular speed (radians/sec). As we typically think of “speed” when boring as the spindle speed, it seems a better form of the relationship. And thus, increasing radius while maintaining a constant spindle speed does increase centripetal force. If you think about a certain surface speed of the cutter, then using that speed over a larger radius logically reduces the force, as it slows the angular speed (rpm).
 

Titanium Knurler

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I really didn't mean to go into boring on the mill here. I simply wanted you to know how to think about your tooling because I guarantee you that one day your mill will begin to move when boring a hole.

Of course, that relationship above is in terms of linear velocity. If one considers angular velocity, centripetal force is m*r*ω^2, where ω is angular speed (radians/sec). As we typically think of “speed” when boring as the spindle speed, it seems a better form of the relationship. And thus, increasing radius while maintaining a constant spindle speed does increase centripetal force. If you think about a certain surface speed of the cutter, then using that speed over a larger radius logically reduces the force, as it slows the angular speed (rpm).

Mike, I am glad you did go into boring on the mill and happy jwmelvin contributed as well. It taught me something that I wasn’t aware of as a newbie: CF/vibration is reduced by increasing the radius IF you maintain a constant SFM which means decreasing the spindle speed. I think where the confusion arises, at least for me, is that intuitively I think that If I have something “off balance”, like a boring bar, and I extend it outward that will “obviuosly” make the vibration worse. For some reason in this “mind experiment” I do not change the RPM or spindle speed so a reduced vibration with extension of the rod seems counterintuitive. Your formulae make it clear why CF and vibration will be reduced with a larger radius when one maintains a constant SFM. Thanks guys, I am now very slightly less of a newbie.

mickri, sorry if we have hi-jacked your thread for a bit. But it was a “teachable moment” for me, at least. BTW, I really like your project and I hope will keep us posted on your progress. TK
 
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