any good books on machining?

[BeeleJuice]

i work as a metal fabricator by trade. the machines i use are, a bridgeport (that i dont even know what model because i cant find any numbers on it, it has numbers on the motor but i was told you cant fint find the model from it, is that true?) i also run a cnc horizontal bandsaw, lathe, and iron worker. and very little welding.

wondering if anyone has read or seen any good books on using these types of machines?

oh yeah and that bridgeport is top of the line. its back lash is 80 thou on the y and 45 on the x. you wanna talk close tol. talk to me. LOL

[NC Cams]

First thing to do is contact HIWIN or Rockford and buy some retrofit ball screws.

Even ones with rolled threads would be light years better than that.

[Mcgyver]

the standard recommendation would be the two volume Moltrecht machine shop practice. i have it and it is a good general reference. i also like a couple of grade 11 or 12 texts that made their way into my shop, they give good, easily understood overviews. I still go to them as a reference for less frequently performed ops.

NC, you're recommending balls screws for a manual machine? at least I'm guessing its manual from the description

[sanddrag]

http://www.lindsaybks.com

[NC Cams]

Mcgyver: yes and here's why:

Ball screw basics:
http://www.cnczone.com/forums/showthread.php?t=20748

Ball screw treatise, the hard core stuff:
http://www.cnczone.com/forums/showth...?t=8813&page=1

I know of NO high end machines that use lead screws or acmes. If you want accuracy, speed and low friction, you use ball screws.

Since I have a Excello mill with acme lead screws and a Bridgeport with ball screws, the BPT is the clear preference for feel and accuracy -both are properly adjusted and well maintained, especially for their ages.

[BeeleJuice]

yeah it manual. im trying to convince my boss to buy a new cnc hardinge. but i dont wanna go into it with not very much knowledge. my buddy works on the other side of the shop on a hurco machining center and i can ask him a bunch of stuff.

even though its so out of tol. with the backlash i can hold .005 on jobs that only require 1 or 2 holes. but it take a lot of setup time to get it within. our shop does quality work but the BP and lathe are not high percision to say the least. i have experience but would like to know how to do more set ups and run products the right way. eliminating the bull S. make for a good day at work.

ill look into that book and see what its about. thanks

[NC Cams]

I am continually amazed at the economic short sightedness and/or ineptness of some shop managers.

Lets take a reasonable shop rate of $75/hour. In the course of a month, one could easily dink away 10-20 man-hours messing with setups to deal with 50 thou backlash in a lead screw not to mention the OOPS factors in scrap and/or anger. Don't forget the "I don't wanna" factor of guys who don't wanna use that lame, tired machine and look for ways to do anything but.

That easily converts to $750~$1500 of lost productivity in one month and $9k~$18K in a year, not to mention over-priced job estimates that lead to lost sales.

When you do the math, it is stupid NOT to retrofit a ball screw - especially when you compare the cost of the retrofit to that of a new mill - even a metric clone, which in most cases is a throw away.

I went thru the exact same math with my machine tool service guy the last time he was here. He sat there in slack jawed amazement when I showed him why it is cheaper and better to spend $800 for good ball screw bearings on a Bridgeport, than for him to spend 2 days tuning a machine at $100/hr to compensate for the slop in a set of $125 OEM replacement ball screw bearings. Like I said, do the math....

The fitting of ball screws to a tired BPT won't do what a new VMC can do in its sleep. However, it (the screw retrofit) may end up to be a more worthwhile time and money saver and scrap reducer in the short run.

Check out the cost of HIWIN or Rockford screws, do some "what if?" math and see what it REALLY is costing you NOT to fix the machine....

[Geof]

Originally Posted by NC Cams .....I am continually amazed at the economic short sightedness and/or ineptness of some shop managers.....

Your analysis is right on but I think to some extent you are not being entirely fair to all shop managers. It is the bean counters above who question every expenditure and get really upset if it is not 'really necessary'. 'Obviously' the machine is okay because BeeleJuice gets things out to spec so it is a 'waste' of money to upgrade it.

You and me are the guys who control the expenditures and we have the breadth of knowledge to look at the whole picture. Many times in bigger companies everything is so divided up no-one can take an overview. If BeeleJuice is in a small company where the boss should know these things but does not seem to get it then he is going about it the right way. He just has to figure out how to make the boss think it was his (the boss' that is) idea to get a good machine.

[NC Cams]

Geoff: I agree and disagree with your premise.

When I say "shop manager", I'm talking about THE guy who makes the decisions. He is the one who is responsible for MANAGING the company and making the critical decisions. If your name is on the front of the check and/or side of the building, or if you hand out the pay checks, you're responsible.

I know of a machine tool maker who used selectively sized bearings of god knows how many sizes to build spindles. They assembled them, checked them and then refit them with new bearings until they finally got something that met the performance spec they advertised. Forget making ONE spindle by holding tolerance and buying ONE spec bearing. But DO spend double or tripple in assembly costs and ditto that in inventory to build a simple spindle that was essentially the same throughout the life of the product.

Sadly, the purchasing guy was saving money by buying cheaper bearings. Concurrently, the mfg floor supervisor was getting his a$$ handed to him for out of line assembly costs.

Who do you blame? The purchasing guy who did his job or the mfg guy who facilitated the process or the HMFIC who should have known/seen that the goals were in conflict and affecting his net bottom line???? Or the bean counter for not identifying where money was being whizzed away and not bringing the matter to someone's attention.

Sadly, they're all unemployed by now but the HMFIC probably got a golden parachute and the others the golden shaft.

A similar deal took place at Studebaker in the Avanti plant. When the frames came in, there was a guy who was killing himself with a hole saw and drill motor cutting a hole into the frame at some odd-ball place. Thru the whole process, the hole was never used. Low and behold, just before the car was shipped, there was another guy who was taking stamped, outsourced plate plugs from a bin and rewelding the hole shut.

WHen he asked why it was being done, he got the "thats the way we've always done it...". When you have a lot of financial inertia, you can tolerate such waste. However, the smaller the shop, the more critical it is for folks to spend time and money wisely. They simply can't afford to keep doing things the "old way".

This lunacy was observed by the guy who bought the Avanti line in a last ditch attempt to become a car magnate - he did stop the insanity but there were too many other insane and endemic problems for the brand/model to survive.

Point is that SOMEBODY somewhere has to know what's going on on the shop floor. That somebody SHOULD be the manager. Since the manager is responsible for the profitability of the workers he manages, it would seem to be his responsibility to be able to justify the expenses needed to do the job right to the bean counters and/or the people who hold the purse strings.

Yes, the bean counters run the books, but they typically don't own nor do they manage the entire company. In the prior example, Helen Keller could see that it would PAY to fix the machine and the payback would be easily financeable with the cost savings.

Sadly, when a shop manager is too busy bailing water because he's rearranging deck chairs on the Titanic, it's too late to have steered a more southerly course to dodge the icebergs.

The member could use the above examples and math model to do some what-ifs on his own. He can then make the pitch to his shop owner/foreman. If the owner sees the merits, great - he and his workers get access to a better machine.

If he leaves matters be, you can readily gage his attitude toward productivity, profitability, quality and work environment. In a sense, the beatings and abuse will continue until morale improves....

[Mcgyver]

well the Bridgeport and Excello's are both high end machines in their class, at least imo and i've never seen a manual one that had or came with ball screws. I had always viewed ball screws, because of the higher helix, as not being appropriate for manual machines. So far as accuracy goes, isn't a ground acme thread just as accurate as a ground ballscrew, certainly it would be better than rolled ball screws. Either type of screw can be just as accurate as the other, there are obviously advantages to ball screws for cnc but how so with a manual machine. I can see the lack of holding power being an issue as well as the decreased resolution resulting from the higher helix, then again I've never used a ballscrew manual machine - you converted both of yours and they're manual? mind you, i can see how you'd have to pimp a bport for it to take preferance over an excello

[NC Cams]

Both machines are in "factory stock" condition and both were bought used from the same shop except for some minor "tune-ups".

The BPT is an Eztrak that was used half-n-half CNC and manual. It was in pristine condition when I got it BUT there were some issues with backlash even though it has a ball screw. Having had machine tool bearing design experience, I started working on eliminating hysterisis therein. It was good as-is and it is DEADLY accurate now.

The Excello was in very good shape but has an acme screw/bronze nut deal in it. It is fitted with a DRO which I initially though was dead nuts accurate. Sadly, I learned lessons about loose gibbs and backlash along the way and figured out how to "tune-up" the system. It is good but not as pleasureable to use as the BPT.

The helix on the BPT is exactly the same as that of a manual machine - 0.100" per rev. All they did was fit servos to a manual machine on 3 axes. NOthing more than a traditional Bridgeport with a "brain" and tireless motors on the axis that follow its directions.

When you run a preloaded ball screw with HEAVY preloaded precision ABEC 7 ball screw bearings (480 lbs in our case), the table actually moves with the same or LESS drag than the OEM bearings (long explanation about internal pressure angle of true ball screw bearings versus OEM bearings) with concurrently more "feel".

When you turn the handle, the BPT table simply MOVES. Backlash is now measured in 0.0001"s, not 0.010"s. DEADLY accurate is putting it mildly. At this point, what used to be the prefererred mill (the Excello) is now the secondary choice.

We've yet to see a case where the cutter will override the screw on the BPT, even if we forget to set the table locks and bury a tool into a part - machine stalls or rotates the head out of position but table don't move.

If you've never used a ball screwed manual machine, you'd probably better not ever try. You may never want to use an acme screwed one ever again, especially one with wear/slop.

[BeeleJuice]

nc cams, i admire your knowledge. i had a few beers today and dont wanna say the wrong thing or have to many typing errors to comprehend. but you are now my new long lost factory worker.

you hit so many nails on the head i could mistake you for a carpenter. LOL. hopefully tommorrow on independece day tommorrow i will get to reply with some questions and praise.