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Evaluating bridgeport ways and what to do about them

After purchasing it, I realized it was the Bridgeport of contentious discussion in this forum haha:

canadianhobbymetalworkers.com

Colchester Student $3500 Calgary

https://www.facebook.com/marketplace/item/2147046365446629/?ref=browse_tab&referral_code=marketplace_top_picks&referral_story_type=top_picks Same seller has a bridgeport for $5000. Both are in the basement of a house.
canadianhobbymetalworkers.com canadianhobbymetalworkers.com

I'm into it for about $5K which included a bunch of accessories and more importantly delivery.
 
Getting a name brand mill with some wear and a little Y way damage, you did fine.

My big mill (clone) has .050 backlash, and I paid a lot more to get it to my door and running. I had to make a VFD setup to run it -- and my X axis has more wear on it. I bought an extra X axis nut for it, but have not needed it yet...
 
Xyphota said:
This is my plan! I am not really interested in scraping anything, except for maybe adding some scrapes to the vertical ways for oil adhesion as per Dabbler's comment above, but I think that will be a later problem.

I think the x-axis at the dial had about 0.020" of backlash, I did not note the y-axis before disassembly. I removed the lead screws and they appear visually consistent throughout the screw, but I dont know how visually obvious it is if a screw is worn out. Fortunately the mill came with a DRO for X and Y so I am to believe backlash shouldn't be a huge issue? I understand the bridgeport machines use split nuts for backlash adjustment. Assuming the leadscrews were in good shape, what would be an acceptable amount of backlash?
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The typical check marks that are put on the ways to hold oil are called "Flaking".

20 thou of backlash would not upset me one iota. Ya, everyone wants less, but machines wear if you use them. So if you don't want backlash to creep in, don't use your machine. 100 thou would bother me a lot. 50 thou would bother some users, but those with good skills would prolly be happy. Some Bridgeports have adjustable leade nuts, some don't. You can tell looking at them. Post a photo if you want help deciding. But keep in mind that a tight nut prolly won't work at the ends of your travel. You have to find the right balance.

If you cannot easily see that the threads are thicker at the ends than in the middle, the screws are not worn enough to worry about. Again, post a photo. Or use a Caliper to measure them at some common point on the thread profile.

If you have a DRO, you don't need to worry about where you are, but you still need to learn to accommodate whatever backlash is there when you are machining. It is easy to break an endmill when the machine decides to take up the backlash on its own. Ask me how I know. It's a very bad experience that can easily destroy an endmill and ruin a part. The bigger the machine, the worse the experience. So ya, learn all you can about climb VS conventional milling and locking the Gibbs on the opposite axis from the one you are using. These are important fundamental pieces of knowledge.

So far I think you have a great machine that you will LOVE using!
 
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The lead screws and nuts are quite greasy so once I clean them I'll share some pictures. I'm reading through the bridgeport manual and it says the lead screws are to be lubricated with way oil. Is there a local supplied that sells Mobil Vactra No. 2? Some online research suggest that ISO 68 oil commonly used for compressors (and available at canadian tire) is an equivalent oil if it is free of detergents.
 
Backlash occurs in two locations, the nut on the lead screw, if adjustable tighten it to the point where it moves freely without binding, if not slit it and make a split nut and adjust it. The second is in the bearings for carrying the screw and how the screw is attached to those bearings. Snug those up without causing binding will remove play.

As an example I have a BB mill and when I did the CNC conversion cleaned adjusted everything. The play on my machine is less than 0.004 ( if not better). On a recent job the I had the mill machining 0.5" hole with a 1/4" end mill, measured hole size 0.4995 to 0.5010
 
Xyphota said:
The lead screws and nuts are quite greasy so once I clean them I'll share some pictures. I'm reading through the bridgeport manual and it says the lead screws are to be lubricated with way oil. Is there a local supplied that sells Mobil Vactra No. 2? Some online research suggest that ISO 68 oil commonly used for compressors (and available at canadian tire) is an equivalent oil if it is free of detergents.
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I don't agree with that. ISO 68 oil is not the same as way oil. Way oil has additives in it to make it sticky.
 
Xyphota said:
I understand the bridgeport machines use split nuts for backlash adjustment. Assuming the leadscrews were in good shape, what would be an acceptable amount of backlash?
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Yes, they do. Manual says set backlash between 4-5 thou.

A861768C-3C8E-4754-9DE6-67B4557F7B93.jpeg
 
As a note - somewhere on here I did a change out of the feed screws and nuts on my mill and did some explaining . I did this as the backlash was unacceptable to me and was hard to drive a power feed as towards the end of the table it was rather stiff. Setting a sloppier fit resulted in horrible operation of the power feed as it would be great at the ends and fly like the dickens in the middle.

With a new x and y axis feed it is like a new mill.
 
RobinHood said:
Yes, they do. Manual says set backlash between 4-5 thou.

View attachment 24879
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When I adjusted my split nut, I had no information (re service manuals) it was take it apart see how it works. My spec was simple, least amount of backlash possible without restricting motion across the entire range. I do suspect that this will reduce the life of the split nuts and lead screw as it loads both side of the thread constantly, a little play greatly reduces this.

In my case it was simple, expect to put in ball screws as a replacement at some point, currently maximize performance and accuracy.
 
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