Advice regarding my worn nuts

[dieselsamurai]

I think after 40+ years I thought it a good Idea to have a strip down and check how bad my nuts were on my mill/drill i mean as climb milling has never been on the cards and accuracy was almost within reach

I always planned to sell it when I got my Bridgeport but its always been difficult for me to sell any tool and 1 mill just doesn't seem enough now, Its been really handy for heavy drilling and with the 2 axis dro I'm fitting it will be of more use im sure.

Turns out after a stripdown that the X axis nut was loose hence the large amount of backlash I was hoping that it meant the nut wasnt worn but looks like it made it worse as rocking side to side has ovalised it too



Should be an ACME thread but they are super sharp now



Both nuts are worn X way worse than the Y but unless I can find some like above i need to make some replacements

An evening of light googling and for what seems like a fairly common Milling machine there are no replacements available from what I can see

If anyone knows a source i would be happy to here from them !

If not looks like the thread is Acme form as stated above at 10 tpi the screw is 23.4mm or 0.920" dia so I can make a nut on the lathe



Screw looks ok not as bad as I expected, whats the best material bronze or brass ?

 

[dieselsamurai]

This is a very similar machine to mine a RF30

 

[Agroshield]

ACME threads come in certain common pitch and diameter combinations. Most machine tools do not use one of those standard combinations. You are quite lucky in that you have quite a large diameter and quite a fine pitch and that makes screwcutting the nut a little easier as a large screwcutting bar will fit in the hole.

Being an overseas machine, there is some chance that the thread form is trapezoidal (loosely 'metric ACME'), but cut to an imperial pitch. It won't make a lot of difference, but a 2.5mm pitch trapezoidal insert from Ali might be cheaper than a 10 tpi ACME insert. Check the hand of the screws as you might need both left and right hand inserts and holders.

FWIW, I would bore out the existing nuts, soft or silver solder in a slug of bronze (research what grade - some are nasty to cut) and then rethread. I think you can get hollow cast bronze bar, which would be economic in material. I guess you know that the slot and capscrew is a backlash adjuster so you can saw that in afterwards. Take a little care to establish the centre of the hole relative to the rest of the nut before removing the old threads.

 

[dieselsamurai]

Thanks yeah I did think its pretty close between acme and trapezoidal thread (1 degree i think) so will look into that I might even have some inserts somewhere. Y axis is lefthand thread will be a challenge but plenty of info out there on doing that.

I did think boring would probably be the easiest solution in some ways but center finding and work holding will be the biggest problem , I may have to dig out my face plate

I just find it odd that for a machine sold in the thousands no one seems to make or stock replacement nuts

 

[Seadog]

I think after 40+ years I thought it a good Idea to have a strip down and check how bad my nuts were on my mill/drill i mean as climb milling has never been on the cards and accuracy was almost within reach

I always planned to sell it when I got my Bridgeport but its always been difficult for me to sell any tool and 1 mill just doesn't seem enough now, Its been really handy for heavy drilling and with the 2 axis dro I'm fitting it will be of more use im sure.

Turns out after a stripdown that the X axis nut was loose hence the large amount of backlash I was hoping that it meant the nut wasnt worn but looks like it made it worse as rocking side to side has ovalised it too

View attachment 486271

Should be an ACME thread but they are super sharp now

View attachment 486273

Both nuts are worn X way worse than the Y but unless I can find some like above i need to make some replacements

An evening of light googling and for what seems like a fairly common Milling machine there are no replacements available from what I can see

If anyone knows a source i would be happy to here from them !

If not looks like the thread is Acme form as stated above at 10 tpi the screw is 23.4mm or 0.920" dia so I can make a nut on the lathe

View attachment 486272

Screw looks ok not as bad as I expected, whats the best material bronze or brass ?

I recognise your nuts. Mine look exactly the same
The X axis usually gets worn more because it's almost impossible to lubricate it.
I'm in the process of converting to ball screws.

 

[dieselsamurai]

I recognise your nuts. Mine look exactly the same
The X axis usually gets worn more because it's almost impossible to lubricate it.
I'm in the process of converting to ball screws.

Im sure many people have nuts that need investigating

I had thought about a full replacement but this machine is really only going to be used for drilling and light machining , I just dont have the money spare to justify ball screws at the moment

A CNC conversion in the future could be on the cards but they are just too far gone to put back in , having full measurements of the nuts might come in handy for that though later on

 

[Seadog]

The other problem is that they're a bastard size. M24x2.5 I think

 

[RichardM]

I repaired the nut on an old Abwood vice with a brass insert soldered in, easy enough to do.
If the nut proves difficult to hold for boring try soldering it to a block for holding.

 

[Agroshield]

I did think boring would probably be the easiest solution in some ways but center finding and work holding will be the biggest problem

On the one with 'wings', it might not be too critical. You could shim up or reduce down the wings to move the nut up and down and slot the holes to adjust it left and right.

Up and down on the other nut can be done the same way. Left and right would need some thinking.

If you had a tailstock chuck, you can hold a bar turned to the minor diameter of the nut, slide the nut onto it and then grab in a headstock four jaw where it sits. This would also be doable with a centre in the tailstock and a fixed steady (set the steady good and tight to the bar when it is in the headstock chuck), but you need something to pull the bar against the tailstock centre (jubilee clip and elastic band to tailstock handwheel).

As above, attach the nut to a 90 degree angle plate using the same threads that attach the nut to the milling machine and attach the angle plate to the faceplate.

 

[dieselsamurai]

A tailstock chuck has been on my list for a while now may need to look into that , from what i remember you can buy a morse adapter ready made for one . I was going to make one but this job was meant to be a quick stripdown so i could 3d print brackets for a dro. Never works out how you think it will

 

[iNf]

You could also try an 'evanut'
https://bbs.homeshopmachinist.net/f...ing-acetal-leadscrew-nuts-the-easy-way/page20

https://rick.sparber.org/EN.pdf

https://drive.google.com/file/d/1dN1N-jCtNV4-Gie4pG3da2FjEVdMFxN5/view?pli=1

 

[Seadog]

There was barely any thread left in the X-axis nut. I did manage to source some 2.5mm inserts but then looked at the lead screw, which was beyond redemption.

 

[dieselsamurai]

There was barely any thread left in the X-axis nut. I did manage to source some 2.5mm inserts but then looked at the lead screw, which was beyond redemption.

I would go down another route but both my leadscrews look hardly worn , of course they are but should be good enough for what i need. Where did you source your ball screws btw ?

 

[Seadog]

Ebay

 

[dave h 2]

M24 x3 or 5 or 8 those are the 3 sizes in Trap which looks like but isn't ACME
Your RF may be graduated in imperial, but the lead screw may still be metric and Trap.
People use brass for leadscrew nuts .
Do not buy Aluminium Bronze.

 

[dieselsamurai]

M24 x3 or 5 or 8 those are the 3 sizes in Trap which looks like but isn't ACME
Your RF may be graduated in imperial, but the lead screw may still be metric and Trap.
People use brass for leadscrew nuts .
Do not buy Aluminium Bronze.

Ive measured the leadscrew and its exactly 10tpi the machine has imperial dials , oddly its a mix of imperial and metric holding it together.

Ive looked online and the price of bronze tube for a short length say 1 1/4"od X 3/4" id is stupid , I have plenty of bronze im sure but most of it it from marine sources so not sure how well it will machine.

LG2 leaded bronze seems to be the best option but I have no way of telling what i have

 

[Agroshield]

...I have plenty of bronze ...not sure how well it will machine.

Try cutting a standard external thread on a piece. That will give you a starting point.

It will all cut; ridgidity of the tool and minimum spindle speed to avoid chatter might be your biggest challenges.

Work out the minor diameter of the thread plus the thread depth (infeed) and that will tell you the maximum diameter of the tool you can use.

With some care, if the material is nasty, you can pre-chase the thread with a grooving tool or a standard vee-threading insert, but aligning the ACME insert to follow the pre-cut groove is tricky.

That is the cost/time balance only you can strike: buy something with known machining characteristics or use something unknown (but the correct colour), taking twice as long on both attempts to produce a worse finished product and halfway through waiting two weeks for a replacement insert.

 

[dieselsamurai]

This looks like the insert i need

16NR 10 ACME T350 Internal Threading Insert for General Use

Carbide Threading Insert Inxternal 10 ACME type 16NR 10 ACME T350 by APT Threading Associated Production Tools Ltd

www.shop-apt.co.uk

im guessing to do the left hand thread will be more tricky need to look into how to do that

 

[dieselsamurai]

I'll chuck up some of what I have later and do some extermal practice threads. Its not a production machine or used for model making so just want to to get the least backlash i can.

Nice little project too although one i didnt expect or need but hey ho no choice now , all the parts are cleaned and laid out ready for inspection etc so got to carry on now

Some people look down on mill drills but they are actually quite usefull machines and quite a lump i think mine tipped the scales at just under 450kg

 

[DAPPH]

Thanks yeah I did think its pretty close between acme and trapezoidal thread (1 degree i think) so will look into that I might even have some inserts somewhere. Y axis is lefthand thread will be a challenge but plenty of info out there on doing that.

I did think boring would probably be the easiest solution in some ways but center finding and work holding will be the biggest problem , I may have to dig out my face plate

I just find it odd that for a machine sold in the thousands no one seems to make or stock replacement nuts

Check Ali Express & Temu .. a few months ago I was about to make my own acme half nuts for my 1943 Atlas / sphere lathe I found the taps for the threads but was waiting till my next months mancupboard money was due ,

A few days later the clever Chinese worked out what lathe I had and produce the half nuts for it , they might soon produce the carriage acme screw nuts too .


Could you grind off half the cutting edge off the tap to leave you with a boring cutter that is tapered ?