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First Boring Head.

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tweinke

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#1
So as you can guess I would like to get a boring head. It will be used on a PM-727 mill. Is there an appropriate size based on the mill size? Also if you could have only one boring head what would be the most useful size. Speaking of size I am working under the assumption that a 2 inch one is good for about a 2 inch bore. Money is an object in this purchase so any comments in that regard would be good too. It would sure be nice if I could find an article related to boring heads that addresses all this but I have had no luck finding what I am asking. Opinions guys? :confused 3:
 

wawoodman

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#2
How long is a piece of string?

I would wait until you actually have a need for one: an actual project. That will keep you from buying one that's either too big, or too small, and having to buy the other one, anyhow. That being said, a 2" is probably a good start. Watch a few videos, and see if you can say "I can see myself doing that..."
 

JimDawson

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#3
A 2 inch boring head will easily bore a 6 inch hole. Most boring heads have a horizontal tool holder position, you stick the boring bar out sideways.
 

mikey

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#4
The bigger the mill, the bigger the head the mill can handle. I don't know what that size is on a PM-727, sorry.

If I could only have one head in my hobby shop, it would be a Criterion DBL-202 head. These come in two flavors, a 202A or 202B; the former takes 3/8" bars and the latter, 1/2". It has three bar positions, two on the bottom and one horizontal position. With bars in these positions, you can bore from 0.050" to 6.687" holes. The holes each position can bore to overlaps so the range is seamless.

The leadscrew is calibrated in direct reading 0.001" increments; dial in 0.005" and your bore gets 0.005" bigger. I have found this head to be well-balanced, very accurate and versatile. They have a 7/8-20 threaded back to accept shanks of various types and sizes, including R8.

Note that boring range is sort of misleading. The larger the bore, the greater the centrifugal and centripetal forces are so balance becomes an issue with big holes. If your mill can go slow enough then you can go bigger - go too fast and the mill will vibrate and can even take a walk across the shop.

Criterion no longer exists but you can buy NOS or used heads on ebay. Brand new, these heads went for close to $300.00 retail but new and used heads in good shape can be had for considerably less. If these heads have a weak spot, it would be the way the dovetail was cut. There is a tiny bit of metal at the base of the dovetail and if the user failed to adjust and use the head properly, the dovetail can snap off so look at pics carefully to avoid buying junk. Make sure all the screws are there and ask if the ball bearing under the gib screws are also present.

The DBL series was one of the most copied boring heads to come out of Asia. You can buy an exact copy for about half what the original cost. Personally, I would go for a Criterion myself. I have two heads from this company and they have been trouble-free and precise.

EDIT: I should clarify that one dovetail on a Criterion head is slotted to create an adjustable gib. The amount of metal at the base of this gib is very thin so care must be used when adjusting it. It is more than adequate for normal use but an ignorant user can eventually snap it off.
 
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Subwayrocket

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#6
With your machine I would buy a Shars. I had a mill same design like the 727 . The accuracy of a higher priced boring head would be negated by a little wobble in the quill and some "give" in the column which all adds up . I have a knee mill now but still use the Shars boring head, it's not too bad. I have been able to get slip fits with it .
 

mikey

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#7
Really, Mike? I can hit it once in a while... ;)
Ummm, well, I mean, it's possible, right?

Okay, okay, the screw is calibrated in thousandths of an inch. Whether or not you can hit it is a whole other thing!
 

4gsr

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#8
......snip...........
Criterion no longer exists but you can buy NOS or used heads on ebay. ......snip.............
Criterion was bought out by Allied Machine & Engineering Corp. in 2013 and still sold under the Criterion label by AMEC. MSC is still selling them. Unfortunately, they are slowly getting out of our price range for use H-M use!

Ken
 
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mikey

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#9
Criterion was bought out by Allied Machine & Engineering Corp. in 2013 and still sold under the Criterion label by AMEC. MSC is still selling them. Unfortunately, they are slowly getting out of our price range for use H-M!

Ken
True, Ken, thanks for pointing that out.
 

tweinke

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#10
Well so far I've learned a lot from you guys, yes I do have a project in mind and will need holes about 2 1/2 inches so I guess a 2 inch may be my best bet.
 

mikey

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#11
If you can swing the cost, Borite cobalt bars are very nice to use in these heads.
 

rick9345

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#12
boring/facing head for future use. Use mine for more facing than I thought I would,no need to tear down and reset on the lathe. Mill becomes more useful.
I have a tree boring head(actually 2) can also bore inside and out side tapers.
 

tweinke

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#13
Remembering that a PM-727 is not a Bridgeport or Kearny and Treker and my budget you guys have inspired me so far to keep looking for a used head and possibly skip the Shars or the like head if I can find something that still fits the budget. More comments are certainly welcomed!
 

petertha

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#14
Borites are very nice & good value IMO. Also, making custom tools from inexpensive offshore boring bars is a viable option especially if you happen to use the same inserts for lathe boring bars (which is what they are intended for).
 

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Subwayrocket

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#15
Remembering that a PM-727 is not a Bridgeport or Kearny and Treker and my budget you guys have inspired me so far to keep looking for a used head and possibly skip the Shars
I would just get a shars . Swap out the set screws and it's not too bad at all . You're never going to realize the higher accuracy of a $300+ head with a column/bench mill . Not rigid enough, play in the quill, column, table adds up. Like I said, I had a bench mill with the shars , now I have a knee mill and still use the shars . I can produce slip fits with the shars head and the dial is actually pretty accurate. I've got a few indexable bars for it now, but the cheap ones they give you work fine. I've bored cast , steel , alum . The Shars boring head is a typical Shars product. Anything i've ever got from them im happy with.
Is their stuff Criterion, Kurt, Yaesu, Sandvik, Mitutoyo ? No , but it's good stuff for the money and not far off the high priced stuff in quality.
Good luck whatever you get .
 
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EmilioG

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#16
With Mikey's help, I wound up getting two Criterion DBL 202B's. One was an original design with a different gib cut that is thicker,
but supposedly more difficult to adjust. I did not find that. In fact, it makes for a stronger head. Both heads are in great shape and were had for
a very good price. I also bought Borite cobalt boring bars. As Mike told me, you can regrind Cobalt bars easier than carbide.
You can't go wrong with one of those boring heads. The ball bearings and set screws can
easily be replaced, and Allied sells a hardware kit to replace these parts if needed. I think these heads will last a long time with proper care and use.
Very solid and well made.
 

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petertha

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#17
I've never disassembled one. Where are the ball bearings located?
 

petertha

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oh, do you mean like a single bearing ball between screw & gib? I was thinking like a ball bearing race.
 

Ken from ontario

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#21
Yes, just a ball between the screw and gib.
Mike would you know if the Criterion s-2 boring head also has a bearing ball between each screw and gib? I looked at the pics closely and it looks like there's no moveable /sliding gib on this model and the set screws force the "fixed" gib to clamp against the boring head body, also there's not enough space in there to fit a bearing ball. :
$_57 (2).JPG $_57 (1).JPG $_57 (4).JPG
 

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4gsr

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#22
Mike would you know if the Criterion s-2 boring head also has a bearing ball between each screw and gib? I looked at the pics closely and it looks like there's no moveable /sliding gib on this model and the set screws force the "fixed" gib to clamp against the boring head body, also there's not enough space in there to fit a bearing ball. :
View attachment 227390 View attachment 227389 View attachment 227392
Looks like that model head does not have the ball installed. Pull one of the set screws or gib screw and see what kind of end configuration is on the screw. You also have to remember the S-2 head is the older design model of the later head mentioned above. still being built and more rigid than the 202 or 203 model in my opinion. Just doesn't have the multiple hole arrangement for boring bars. Ken
 

Ken from ontario

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#23
Looks like that model head does not have the ball installed. Pull one of the set screws or gib screw and see what kind of end configuration is on the screw. You also have to remember the S-2 head is the older design model of the later head mentioned above. still being built and more rigid than the 202 or 203 model in my opinion. Just doesn't have the multiple hole arrangement for boring bars. Ken
Thanks Ken, I haven't received mine yet ,it's just the curiosity is killing me, I'm sure the first thing I'd do is to check under the set screws , I bought this older model mainly for it's size so it would be a good fit for a mini mill and of course the quality in general is supposedly better than the equally priced but imported boring heads.
 

mikey

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#24
Mike would you know if the Criterion s-2 boring head also has a bearing ball between each screw and gib? I looked at the pics closely and it looks like there's no moveable /sliding gib on this model and the set screws force the "fixed" gib to clamp against the boring head body, also there's not enough space in there to fit a bearing ball. :
View attachment 227390 View attachment 227389 View attachment 227392
Ken, the gib does not slide. If you look at your pics, you can see a small vertical slice to the side of the dovetail on the right; the part between the dovetail and the slice is the gib. You can see that only a very small area of metal supports that gib and this is fine in normal use. Just don't go cranking down on the gib screws without the main bar holding section in place.

Yes, there is a small ball bearing under each gib screw. It allows the moving part of the head to slide smoothly in use. There are three gib screws. The center one is to lock the head prior to using the head; it is not a gib adjustment screw. You are supposed to unlock the center screw, move the head to the new position, then snug the center screw to hold it at that setting. You only need to snug this center screw; do not crank down on it. The outer two screws are the gib adjusters; you snug one up until slight resistance to movement is felt and then you do the same to the other. Many guys adjust all three the same way and use the head without locking anything down. This works but is not the way Criterion intended the head to be used.

The S-series heads have a relatively large dovetail contact area for its size, which adds to their stability as Ken said. I have a S 1-1/2 and it is very precise, very smooth and very accurate. Because the bar hole is centrally located the hole size it can bore is limited but it is an excellent head within this range. Although my DBL-202 can do it, when I need to bore a smallish hole I reach for the S 1-1/2. Unlike the 202, my 1-1/2 can extend to the limits of travel without vibrating unless I get stupid with speed.

Don't worry, Ken. You will love this head.
 

Ken from ontario

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#25
Ken, the gib does not slide. If you look at your pics, you can see a small vertical slice to the side of the dovetail on the right; the part between the dovetail and the slice is the gib. You can see that only a very small area of metal supports that gib and this is fine in normal use. Just don't go cranking down on the gib screws without the main bar holding section in place.

Yes, there is a small ball bearing under each gib screw. It allows the moving part of the head to slide smoothly in use.

Don't worry, Ken. You will love this head.
Now it makes so much sense to me, this square shaped boring head shares the same basic design as the bigger round shaped ones as far as the gib/dovetail configuration goes, and both types (round and square) have a fixed body part that resembles a Gib,the set screws pushes on the ball and the ball focuses the force to a single point on the fixed gib and makes it lock against the bar holding section.Thank you Mike .
By George, I think I've got it.
 
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FanMan

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#26
boring/facing head for future use. Use mine for more facing than I thought I would,no need to tear down and reset on the lathe. Mill becomes more useful.
Stupid question then, are boring heads and boring/facing heads two different things?
 

mikey

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#27
Now it makes so much sense to me, this square shaped boring head shares the same basic design as the bigger round shaped ones as far as the gib/dovetail configuration goes, and both types (round and square) have a fixed body part that resembles a Gib,the set screws pushes on the ball and the ball focuses the force to a single point on the fixed gib and makes it lock against the bar holding section.Thank you Mike .
By George, I think I've got it.
Yup, you have it exactly right. Funny thing happened today - a good friend came over for a visit and he brought me a mint condition S 1-1/2 head with a 1/2" Criterion shank in it. Now I have two S 1-1/2 heads.
 

Ken from ontario

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#28
Yup, you have it exactly right. Funny thing happened today - a good friend came over for a visit and he brought me a mint condition S 1-1/2 head with a 1/2" Criterion shank in it. Now I have two S 1-1/2 heads.
That's great, you can never have too many boring heads:D
 
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