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Frank Ford
10-30-2006, 11:12 AM
Yesterday I noticed my mill (Sharp BP clone) had slipped a tiny bit out of tram, so I spent a few minutes setting it straight. When I loosened the joints, I noticed that the bolts seemed less tight than I remembered so I got to thinking about torque.

The question: Approximately what is the appropriate torque for these bolts?

pcarpenter
10-30-2006, 11:28 AM
Frank-- I don't know the answer to your question, but will look at the several bridgeport manuals I have in electronic form for a recommendation.

What I really wanted to write was an anecdote that hopefully will help keep you from getting too carried away. I am fininshing up a rebuild of a BP I bought a year and a half ago. One of the bits of damage I had to clean up was that someone must have used an impact wrench or just got carried away with tightening those bolts on the mill I bought. They are square head bolts and the heads ride in a T-slot in the face of the "ram adaptor". This is of course relatively soft iron and mine had some dinged up crushed areas where the bolts sat. I had to reach in with a die grinder and carefully remove the portion of the relatively soft malleable iron that had been "crushed" by the bolts and smooth things up so they will slide smoothly around as needed in the future. Even malleable iron is more "crumbly" than steel, so don't overdo it. Certainly having the head slip in use could be catastrophic, but no need to do damage in an effort to avoid damage, so all things in moderation.

I guess some folks have this "if some is good, more must be better" mentality. When my father gave me the long break-over bar (1/2" drive) I asked for years ago as a Christmas gift, he said "It goes against my better judgement as a Carpenter to give you one with this much leverage". My Dad always wrung things up tight...then a little more.

pcarpenter
10-30-2006, 11:42 AM
Frank-- this is from a 60's BP manual. It is not very specific except to warn against overtightening as it can cause issues I had not thought about:

"Mounting Head on Overarm Adaptor--

The face on flange or adapter shoudl be throoughly cleaned as this aligns milling head square with table working surface. Then clean mounting surface of head carefully. When bloting the head to the adaptor or overarm, tighten nuts evenly, using normal pressure. Care should be taken to avoid excessive pressure since this will cause distortion in the quill."

so....whatver "normal pressure" is is the right answer:confused:

The newer manual just says "Tighten the four head mounting bolts".

Paul

ERBenoit
10-30-2006, 11:42 AM
If this helps you any......

The manual I have for a "Bridgeport" calls for an initial torque of twenty five (25) foot #'s, followed by a second torquing to fifty (50) foot #'s. The front bolts are sequenced as follows: Lower left, upper right, lower right, upper left.

The bolts on the ram are torqued in the same manner, yet not in a specified sequence.

They do warn that over torquing may cause quill binding. The ony quill binding I have ever encountered is from the quill lock.

No, I do not use a torque wrench when tramming. I have not had any trouble (yet).

Frank Ford
10-30-2006, 02:31 PM
Thanks!

I just checked my bolts, with the torque wrench and I was able to move them just a bit at around sixty foot pounds, so I guess I'm in the ballpark.

Millman
10-31-2006, 02:32 AM
Frank, you say the mill is a Sharp, BP Clone? Remember the quality of the material is not as strong as an old BP. In the old days, the bolts could be torqued tighter than now. In the imports...the PD's and other dims are not to be compared to the old BP's

speedy
10-31-2006, 05:21 AM
I am not familiar with your machine Frank but perhaps, as Millman has stated, the quality is not there. Maybe bolt stretch is the culprit? Can you replace them with higher tensile items?
IMHO cleanliness and an even torque sequence is as important as actual torque value.

kap pullen
10-31-2006, 07:28 AM
I have always thought the Bridgeport to be a finishing machine.

The old cinn, k&t and other heavy duty makes had no adjustments like the bridgeport, except maybe the vertical head accesory could be set on an angle. Yea, there may be exceptions.

When an apprentice boy, (1969) the heavy duty mills could take .25 doc with a 6 inch carbide cutter at nearly 20 inches a minute. Course, you didn't have the quill hand feed for drilling and tapping.

The Bridgeport is really a wimpy milling machine, but very adaptable for light duty work. It has eliminated need for those banks of dratted spindle drills.

I knocked my bridgeport (at work) out of tram the other week taking a cut with a 3/4" end mill 4 " long finishing out the slot in a 304 ss clevis 3.5 " deep.

That is all I have to work with there.

I have to race the clock, and it comes back to bite sometines.

Treat it, and it's clones with the respect they deserve.

Kap

tattoomike68
10-31-2006, 04:01 PM
One time I tightend down a mill spider too tight and broke one of the arms off. (spider the part that locks the main base swivel)

Im not sure how strong you are but when I tighten the swivels or ram down I use the mill wrench that I use on the draw bar and tighten it as tight as I can with 2 fingers pointing strait out.

If I can break it with 2 fingers its a peice of junk. The 2 finger trick works on the drawbar too.

It sounds crazy but it works.

Scishopguy
10-31-2006, 04:50 PM
There is no machine safe from the "young machine operator" with a wrench and a length of pipe. I saw one fella crank down on the bolts holding the work to the table of an old Cinncinnati #2L, so hard that it broke a big chunk out of the Tee slot on the table. It was kind of like the damage to the lathe compound that someone showed here a week or so ago. He would pull on that cheater bar until the cap screws would give a loud "cracking sound." Needless to say, he scored a week off without pay.