Table tram

[NP317]

I use an "EZ-TRAM" ring to span the Kurt vise and allow head alignment.
'Have used one for years with success.

I don't know if these are still aviable for purchase from Accudyne Corp.
RussN

image033.jpg (32.12 KiB) Viewed 2478 times

[pete]

If your "parallels" are like some of mine Bill there decidedly wavy. While there available with both sides and faces ground, most of the more affordable one's sold aren't exactly parallel on those faces at all because that's usually a non working surface. And you should be real pleased with those numbers. Those are better than any average mill can machine the parts to, but being that close doesn't contribute to any further inaccuracy the machine is producing. So to me getting the tram as close as possible is a good habit. Once you're within a couple of thou I use a DTI the same as you do and set the ball tip so it's trailing the rotation direction, that way as you get even closer with adjustments the tee slot spaces don't have much effect as the tip passes over them. But probably most have already figured out the same on there own.

Having that nod feature is handy for tramming and mine has it. But luckily your mill is really close, and as others have said, not having it makes the head mount quite a bit more rigid. So far I've never had to make a compound cut set up using the head, so mines just more of a convenience while tramming than a usable feature. With a fixed Y axis on the head, (no nod) the only way I know of to bring that axis into plane if it's out is to either shim it or hand scrape the high end down until it's correct. I don't know about the numbers for yours, mine has the same stud sizes the real BP's use, so I use the same 50-60 ft. lbs of torque on the nuts there recommendation is. According to some posts on the PM forums, over torquing those nuts on real BP's can distort the head casting enough to pull the spindle bore out of round. It's at least something to be aware of.

[Bill Shields]

i have 2 big blocks that i know are ground parallel that l lay down on the table and use for reference to 'jump' the T slots as you are thinking.

[Harold_V]

I don't subscribe to the use of ANYTHING between the indicator tip and the table. YMMV!

Here's why.

The slightest bit of dust, or a miniscule ding, has the ability to raise the object being used. That yields an erroneous reading.

By allowing the tip of the indicator to make direct contact, even slight dings, dings that might go unnoticed, don't make a difference.

I've lived by that concept as long as I've been in the shop. I also like to use a single cut dull file to draw file the table surface on occasion. I do NOT like to use a stone for this purpose (a stone cuts readily, even on a surface you hope to not modify). A sharp file cuts too easily and can do damage. A dull file, driven by the palms of one's hands, will readily remove dings, yet glide on a flat surface.

H

[Harold_V]

According to some posts on the PM forums, over torquing those nuts on real BP's can distort the head casting enough to pull the spindle bore out of round. It's at least something to be aware of.

I strongly suspect that those posts aren't true. Not suggesting you haven't read such a thing, however.

Take a look at the construction of the head of a BP. The bolts that restrain the head are on areas that are solid cast iron. While cast iron isn't known for its tensile strength, it has exceptional compression strength. In my wildest dream, I can't imagine being able to apply enough torque to distort the bore for the quill. You'd pull the threads long before that occurred.

H

[Bill Shields]

I don't subscribe to the use of ANYTHING between the indicator tip and the table. YMMV!

Here's why.

The slightest bit of dust, or a miniscule ding, has the ability to raise the object being used. That yields an erroneous reading.

By allowing the tip of the indicator to make direct contact, even slight dings, dings that might go unnoticed, don't make a difference.

I've lived by that concept as long as I've been in the shop. I also like to use a single cut dull file to draw file the table surface on occasion. I do NOT like to use a stone for this purpose (a stone cuts readily, even on a surface you hope to not modify). A sharp file cuts too easily and can do damage. A dull file, driven by the palms of one's hands, will readily remove dings, yet glide on a flat surface.

H

you have not seen the table of my milling machine....even after a dull draw file cleanup - looks like the surface of the moon...

was that way when I $$ the mill....came from Redstone Arsenal where then not only dinge / cut the table, but managed to drop the mill on its side and crack the motor mounting frame.

long story -> but a good $$ on the mill....meets my needs...

[pete]

Well my guess is there has to be some truth in the advice. Those guys on PM aren't known for believing in fairy tales, and I've read it mentioned by more than one poster without anyone challenging it. I'd prefer to err on the cautious side instead of finding out the hard way Bridgeport has some good reasons for a recommended torque range on those nuts. The fit on a good mill between the spindle and bore is a whole lot tighter than something like automotive crank shaft bearing blocks, and those have some pretty specific limits on there +- torque allowance.

[Harold_V]

All I can say is I've owned two BP mills in my many years, both of them purchased new. I have never torqued the bolts, but I do tighten them securely with the provided wrench. I'm not a strong person, and I'm not "ham handed". I have a decent sense of what "tight" means and can securely tighten ¼" screws without breaking them. Note that I own three torque wrenches.

That said, the quill on both of my machines can be advanced easily and retracts of its own accord, depending on the location of the handle. At no time have I ever experienced any type of unusual friction, which I suspect would very much be a part of distortion of the quill housing due to over tightening.

I do not suggest that torquing isn't a good idea. I fully agree that it's better to be safe than sorry. However, in this case, I suspect that the torque value provided by the maker is one that safely locks the pivot so it can't be moved under normal use, and not do any damage, not to prevent distortion. I certainly could be wrong.

In regards to torque on crankshafts, it has nothing to do with bearing fit (and if it does, something isn't right). It has everything to do with enough restraint that the bearing cap can't move, or the bolts to work loose. It, like the head of a BP, clamps against solid iron, and would be extremely difficult to distort with the provided bolts. Limits are placed on those fasteners to ensure that they are tight enough, but not too tight, which offers the chance of pulling the threads or stretching the bolts.

H

[LIALLEGHENY]

Harold,

Overtorquing the main bearing bolts will distort the main bearing caps, thus changing bearing clearances. Engine manufacturers always recommend replacing maincap bolts as well as head bolts as they are designed to stretch. In higher HP builds it is recommended that studs replace stretch bolts, and in all cases line boring be performed during the rebuild process. Torque plates should also be used when honing the cylinder bores, as the cylinder heads will distort the block as will the head bolts pulling on the threads along the cylinder walls.
In matters relating to milling machines, especially CNC machines using CAT or BT tapers, I was contacted by a company trying to sell pull studs that are longer than standard ones, but without the last 2-3 threads closet to the shoulder. The idea being that the standard pull stud distorts the tool holders taper closest to the stud, and having a deeper engagement elimates this distortion. Don't know the truth behind this or if it's just another sales pitch.

Nyle

[Harold_V]

Nyle,
I question the validity of that claim. Cast iron rivals steel in compressive strength and can be on the level of 200,000 psi (100 tons). That's one hell of a lot of tonnage. A far greater amount than one might achieve with relatively small bolts, too be sure. Bearing caps, in particular mains, have a serious amount of surface area. I'm having a hard time coming to terms with the idea that the bolts can alter bore size, when they bear ONLY on solid material. That's a lot of material to displace or distort.

My questions is, is this proven in fact, or is this one of the things that everyone loves to say, but is not based on fact? I welcome anything you can provide in the way of a learning experience for me.

By the way, I sure have enjoyed those Kennametal tool holders. Thanks again.

H

[LIALLEGHENY]

Harold,

I can speak from personal experience. Buddy of mine rebuilt a Ford tractor engine, without using a torque wrench. Assembled the whole engine and brought it to me because he couldn't get it running. Thought the cam was out and asked me to check everything out. I could barely spin the engine over on the stand. We pulled it apart and the moment he started breaking the main caps it all freed up.....he didn't have this problem before the rebuild and used the same crankshaft, just had it polished. Took the block to the engine rebuilder who confirmed the mains now needed to be line bored.

Nyle

[Bill Shields]

Maybe BP is concerned about the bolts either coming loose or being stretched / broken as a result of improper torque?