Changing the x-axis spindle and nuts -Bridgeport type mill

[Brent H]

Hey folks,

So I bit the financial bullet and thanks to @Chicken lights making a pick up and delivery I was able to get a new x axis shaft and nuts for my circa 1981 Bridgeport. The combo was about $300 US so not for the squeamish and it took a bit to convince myself to get it. Essentially the spindle and nuts I had were pretty good - backlash in the middle of the table was acceptable and my cheap o power feed did the job well. There is always a “but” and my mill has a 42” table with 36” ish travel. When things are hard to move about 12” either side of centre I thought replacement was necessary. You could hear the power feed bog down and the speed drop and @Chicken lights said he would make a stop and drop - sweet!!!
The change out is fairly straight forward if you have a few things you can use. The table is bloody heavy and slides like a figure skater on ice - amazing actually. I have an adjustable roller table for my sander outfeed that you can adjust to take the load. I recommend not sliding the table full off unless there is a need.

tools are pretty simple, however, I do have a 24” screw driver (princess auto) for adjusting the backlash. My wife also donated a felt hat a few years ago for wipers and the remains fit the bill for the felt spacer you need between the split nuts. Yes, your long shaft will be riding split nuts with a soft felty area for lubrication - (minds out of the gutter!!!)
I installed a cheap Chinese power feed last year so the install will reference that as well. I can expound on that if there are some questions.

I will start the whole process in my next post - I reduce a bunch of pics to a better posting resolution.

 

[Brent H]

So here is the victim:


Remove the boards and the vice and then remove the power feed. Power feed comes off with Handle removal (3/4” wrench) and 4 Allen head screws. Keep the spacers and bearing race that is fitted.

I then ran my x-axis down until the left hand side was a few inches from maxed out. Then take apart the double bearing side.


You may need to use a puller and the locking nut to pull off the spacer over the key.

The double bearing housing came off with a few gentle taps after removing the 4 Allen head bolts. Sould not be a big time tight fit. Just a tap type fit. To pull the keys out- they are woodruff type and I just pick a side and tap around until a set of pliers or vice grips can persuade the key out.

 

[YYCHM]

I guess this means your home again? When you say spindle here are you talking lead screw?

Craig

 

[Brent H]

I guess you can say that - since there is effectively 3 axis movement I gather “lead” can be a bit ishy. On a lathe the lead screw is pretty much it - you are going one way or the other in the x axis. Then you got that y- axis “feed” screw but really no z to complicate -...... hmmmmmmm

I changed the y axis earlier this year on the mill as I was slicing some cast iron with a 1/4” slitting saw and things went rather jumpy with a negative result on the mill.

to keep it simple - x axis spindle - y axis spindle and Z axis spindle - will try to keep that nomenclature as it is confusing to me as well.
I have been machining parts for the Cincinnati and can update that post soon and - man - shafts, spindles, posts bearings bushings - argh!

 

[Brent H]

Will measure my longest cast iron pieces for you - post tomorrow

 

[YYCHM]

Ya, lead probably doesn't apply here. In my RF30 manual there are referred to as table screws?

 

[Brent H]

To make the table easier to slide you need to back out the gib. To do this it is just a matter of loosening the gib screw until it and the gib can come out. The X-axis is locked using a simple lever that screws a bolt into the gib and presses the gib tighter into the dovetail. You can see that my gib has a bit more wear in that particular area. You can also see the original scraping marks to allow oil to be retained on the gib. The gib also has oil passages carved in to it.



To remove the x-axis spindle you also need to remove the backlash adjustment screw and the retaining screw. You can do this with a long screw driver or slide the table off and do it from the top.

table slide off using the support roller table. I additionally clamped the table legs in case the weight was too much.

more coming..,

 

[YYCHM]

Is that a rotary table I see in the last image? How much does that sucker weigh?

 

[Brent H]

With the table slide back you can see the Feed nut bracket and access the backlash screw. I removed the locking screw and the backlash screw.


you can see in the first pic the ways on my mill are chromed and have retained much of the original oil scrapes. This was an other reason to replace the screws as the mill is still in super shape. Once the backlash screw is out you can then use the x-axis screw to knock the nut free. It is held from rotating by a key - the key should stay in the feed nut bracket.

The little tubes are for the Bijur oiling system. While the top was pulled back I pulled the pump lever to make sure oil was being delivered to all the spots I could see.
More coming. ....

 

[Brent H]

@YYCHobbyMachinist

Is that a rotary table I see in the last image? How much does that sucker weigh?

Yes- that sucker is a 12” vertex with an 8” bison chuck mounted. It weighs in at about 250lbs. The table alone is 185. What you cannot see in the picture is that there is a beam running above my mill that I bolted a lift bracket to and I have a 1/2 ton chain fall I use to lift that sucker onto the mill. A 10” or 8” would have been preferable but I bought that sucker complete for $350. I added the indexing plates for $150 - very hard to find in Canada and I got them in the US. I have a few more blanks to make and then that puppy will be back on gear detail.

 

[PeterT]

Great pics, appreciate the documentation!

The X-axis is locked using a simple lever that screws a bolt into the gib and presses the gib tighter into the dovetail.
My CI lathe gib had semi circle little bite marks where the tightening bolt engaged despite just being hand tightened on a small knurled knob. I always thought this was a bit primitive but maybe its the common way of locking the table. I guess if its marring the opposing face of the gib strip its not really all that critical. I came up with something different using a brass foot on the end of the bolt with a wedge angle to match the strip, more contact area etc.

Does your mill have just 1 tightener? (My BP clone has 2 on either side of center)

 

[Brent H]

Here is a comparison of the old style axis nuts and the new split nut design. The old style has some slots cut and a recess for the backlash screw. Tightening the screw would deform the nut and take out backlash. The new split nuts pushes the nuts onto the screw to remove the backlash. Between the split nuts I added a felt spacer to align the key ways and to add a place for oil to soak in and lubricate things. It is a band of felt verses a washer as the key way needs to be clear.
Once the nuts are on and aligned you can slip the shaft back into place - be sure to keep the key way aligned. Also pay attention to the shaft ends as one end has a longer bearing area and that goes on the left hand side. The single bearing side is where the power feed goes. Once nuts are seated (may take some gentle taps on the spindle end) you put back in the backlash screw and the lock screw. I tightened up the backlash screw until there was no real end play and locked the screw. Everything spun super nice.
Reassembly was the reverse operations. Once the table is slide back to expose the left side of the shaft you pull the table towards yourself to allow the gib to be slide back in. Put the gib screw in as the gib is going into place and tighten up close to original. I coated things in way oil as I reassembled and make sure no particles get between faces.
More coming .....

 

[Brent H]

@PeterT - yes I only have the one lock and the y and z only have one. It could be due to the lubrication system? I set the gib up so that it is tight and the table slides nicely and locking the x-axis does not result in any y- axis change on the dro.

when I got the mill I was amazed with a few things:

1. totally dirty
2. Owner had no lubes
3. Owner had no clue how to operate all the features
4. There was a bunch of tooling (the basics to get going) and they had not been used by the owner
5. It was $2900 and I think I paid 2600

I would hazard a guess at another $3000 I spent on tooling, parts and materials including for the lathe - I had to get a new vice so next to the a axis feed screw that would be the single biggest cost.

 

[Brent H]

I will finish off the installation post later today - got a few things to get at....LOL

 

[YYCHM]

What does your vise weigh? That sucker looks as big as the rotary table LOL.

 

[Brent H]

I think about 65 to 80 lbs. feels like a sack of cement when carrying around - which I try to avoid

 

[Brent H]

The lift set up for the rotary table :



Putting the left side of the mill back is fairly simple. Slide the table over to expose the shaft.

clean up all the faces. That paint marker is original as far as I can tell. Put the double bearing back on - couple love taps might be needed. Then the key can be tapped in until it seats. The four socket head screws line up the bearing holder - some mills will have a dowel pin(s) mine does not.
The spacer/ graduated dual holder goes on over the key - might need a bit more persuasion.

Once it is on you can re-install the handle and nut (3/4” wrench). Then we do the power drive end if you have that......

 

[Brent H]

The overall shaft I found (the new one) is about 1/8” shorter and this caused me some grief with the power feed. Using the left side crank the table over to keep the shaft to the new nuts length short - it will help to align things. The new power feed has slotted bolt holes and can move up and down a bit. Install the bearing spacer and slide on the power feed


You will need to install shims to space the driven gear properly. The gear must engage and not bottom out. It takes a few tries. Apply some grease to the gear. Put in the key and then install the bronze gear. Due to the smaller length of shaft my handle would not fit - or at least the nut would not go on. I machined off 1/8” of the bronze gear and put things back on.

After this I checked for backlash and operation - runs about 3-5 thou and is constant through the full range of the table

 

[Chicken lights]

Great! Glad to play a small part in getting this fixed up

 

[Brent H]

@Chicken lights - thank you again!! She is almost a new mill