Living with a worn machine
|Matthew Davenhill||28/05/2018 22:47:18|
|16 forum posts|
I’m in the process of stripping and cleaning a Bridgeport j2, all works but showing a fair amount of wear. Other than scrapping or re scraping the ways, any advice on working with worn machines?
|Mark Rand||28/05/2018 23:15:43|
|625 forum posts|
Re-align and re-scrape all ways. Make new (adjustable) feed screw nuts. Check and, where needed, replace all bearings. Make new gibs, as needed. make replacement pulleys if needed. Fit one-shot oiling system to prevent pervious abuse recurring.
Enjoy using like-new machine.
It's quite fun, once you get into it.
|David George 1||28/05/2018 23:16:38|
578 forum posts
Hi Mathew I have had quite a lot to do with resurrecting Bridgeport mills I dont know how worn or how much wear you can live with but normaly the leadscrew and nuts for both axis can be remade on a lathe or bought from hardinge Bridgeport as quite alot of spares are still available. If the available adjustment has been used up on the jib strips you can mill a pocket in the back and insert a strip of gauge plate to increase the thickness after checking gap with feeler gauges. The Z axis usually dosnt wear a lot on the jib but the nut can wear quite a lot and if it should fail may drop vertically. Make sure that the lube system works and one of the jobs to clear and repair pipes etc. I have a copy of the handbook including service details and part list on DVD and if you want a copy send me a message where to send it.
|Matthew Davenhill||29/05/2018 21:56:31|
|16 forum posts|
Some indication of wear, can see some remnants of scraping on the rear slide, thanks for the advice both.
David- I think I have a copy in pdf format, also have the lion industries book. Don’t really want to scrap it, more because I’m not sure where to start!
2904 forum posts
There are loads of BP manuals for free on the internet, not least from the actual Bridgeport site itself, as well as all manner of (free) rebuild vids and logs.
If the leadscrew is worn, the backlash will vary along the length, being worst near the middle where it has seen most action. So there's little point getting carried away with new nuts and adjusting them carefully. If you almost eliminate the backlash near the middle, you will simply bend the adjuster screws when you first move away from the middle of travel. The nuts are only a part of the problem.
One option is to simply replace the leadscrews and the cheapest route may be to get some rolled ballscrews from Aliexpress, machined and ready to drop right on. Did this on mine and they are fine. Of course, the table wear is still there, so it's not a magic fix. I'm sure there are people who will tell you you can't use ballscrews on a manual machine but you'd have to be a bit dull to find yourself unable to use them and perhaps shouldn't be loose in a workshop in that case. I like them.
I couldn't see any justification for regrinding the ways on my machine. You couldn't seriously scrape the wear away on a typically 42" long table (and that's just the X axis) - if it's bad enough to need attention, it will surely require machining as a first step.
The biggest improvement I made was fitting a DRO, since you can work around almost any level of backlash by tightening up the slides a bit and reading off the actual position. I can do some pretty accurate work on my fairly worn machine by taking care. I'm not a willy waver but I can achieve the levels I (and most of us here) need.
|Mark Rand||30/05/2018 10:27:45|
|625 forum posts||
My 10"x48" Beaver VBRP table was hogged 10 thou and worn 3 thou. Up to 8 thou on other ways. All scraped out. Perfectly possible. Helps immeasurably if you've got a Biax scraper though... .
Edited By Mark Rand on 30/05/2018 10:37:24
714 forum posts
Matthew it depends on what you want and how much you wish to spend but Terry Braithwaite restores Bridgeports and has an excellent reputation : -
Braithwaite Machine tool Restoration
We purchased a fully restored machine from Terry many years ago and have to say it is superb. I think he worked at Adcock & Shipley originally. He may be able to help with just the scraping ? Only find out if you ask !
|Neil Wyatt||30/05/2018 18:25:31|
15223 forum posts
You should mention why they aren't normally recommended for manual machines - they are less able to 'self lock' so unless you keep a hand on the handles the cutter can pull into the work.
|Chris Evans 6||31/05/2018 08:54:23|
|1320 forum posts|
A bit of research across the lead screw manufactures sites should come up with suitable leadscrews and nuts suitable for modification to fit. You will have to turn the ends of the screws to suit but a simple enough job and very cost effective. My machine is metric so a little more choice of supplier, I have "Y" axis cross slide screw from an import machine that will one day be modified to suit my Bridgeport, the nut I will most likely have to make. I bought a 1 metre length of trapezoidal leadscrew for my lathe cross slide enough for three screws I think it was less than £50
Edited By Chris Evans 6 on 31/05/2018 08:55:22
|464 forum posts|
they are less able to 'self lock' so unless you keep a hand on the handles the cutter can pull into the work
In theory. In practice, they work fine - more than enough drag through the slides so pull-in isn't a problem on a Bridgeport-sized machine. None moving axes would be locked via other means, so not an issue there.
I put handwheels on ballscrews on a Taiwanese CNC kneemill at my last employment & ran it as a manual machine for years without any problems using HSS drills, endmills & a 50mm 3 insert face mill. As the machine was built as a CNC carcass it had Turcited ways, so should have been more prone to pull-in if anything - again theoretically, as in practice it didn't happen.
|Mark Rand||01/06/2018 01:07:47|
|625 forum posts|
Another thing about ball screws is that they don't have the backlash that causes problems on clapped out machines in the first place. It isn't so much that the 'low friction' ball screw will encourage bad behaviour when climb cutting as the lack of any restraint with loose gibs and much backlash allow it.
With a Bridgeport sized machine working within its design range (1-3 hp) there's enough inertia and friction to prevent excitement, providing the clearances are close to the original levels.
Something like a myford ML7 with vertical slide and an 18mm cutter in the mandrel is a completely different kettle of fish. DAMHIKT...
Edited By Mark Rand on 01/06/2018 01:10:04
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