# Acetal / Delrin cross slide lead screw nut.



## Dranreb

I think there is a thread about doing this on here but can't find it, If anyone knows where it is, would they be kind enough to post a link in this thread?

Having read about the Delrin method of making new nuts I thought I'd give it a go, as I had a lump of Acetal handy,  my first attempt had alignment issues..







My second idea was to drill the hole, hacksaw the block in half, but stop the cut at a point which would leave the spigot part whole. Then I wound the screw in which forced the halves apart, I was much more careful with the heat this time and it was successful. I used a spare worn screw.




After the melting and taking it off the screw, I tapped a knife into the cut to open it, then used the screw with a ground flat on the first thread to clean the thread so that is turned the full length easily.




Using a tight fitting drill for alignment I turned the sides and end face to be square with the screw.




Only very slightly loosening two jaws, I swapped ends it  in the chuck, I drilled and tapped the center, I drilled right into the lead screw hole as I wanted to use a much longer fixing screw as I didn't thrust the spigot not to snap off, this way it is just a spacer.




I put a screw in the hole before turning the spigot to stiffen it and avoid flexing, I thought had hacksawed too far but you can see there was just enough uncut left if I made the spigot a tad longer than  the original one, more careful measuring here is the only thing I will do differently when I make another for my turret slide.

Two holes then drilled for self tappers, I opened up the top part for clearance, putting a hack saw blade in the slot as a stop to prevent drilling into the bottom half, and countersunk them.

Rounded off the end with an angle grinder and finished it by hand filing.




It only took a morning and I now have absolutely zero backlash!

 It works OK dry but with lube it's silky smooth...way to go guys, get it done!!!

Bernard


----------



## bvd1940

The way I remember the write up the guy used the old half nut, bored it out, fit durlin into the old half nut bored it out so it was somewhat smaller bore than the lead screw ( I think it was 1/2 the depth of the threads) put it on the lead screw and heated the lead screw while clamping. (do that make  since to you?  Hard for me to explain with words. Try a goggle search for half nut fix should find the write up.


----------



## Dr.Fiero

I realize it's not the total DIY route, but....

When I was building my first CNC router/engraver/mini mill, I wanted no backlash (or super minimal!) to contend with, but didn't want the expense of ball screws.
So, I went with these: http://www.dumpstercnc.com/acme_menu.html

They're still in there, and work great!  Just make sure that you have NO burrs or sharp bits on your screws or you'll eat them alive in no time.


----------



## Smudgemo

Hope I don't get into trouble here, but this thread (from another board) has a ton of information on this subject.  Makes me want to try it for my cross slide nut as it's got plenty of slop.


----------



## Dranreb

Smudgemo said:


> Hope I don't get into trouble here, but this thread (from another board) has a ton of information on this subject.  Makes me want to try it for my cross slide nut as it's got plenty of slop.



Thanks Smudgemo, that's the original source, i felt sure it has been discussed on here though.. 

I've been using it quite a bit and found one problem, because I thought a longer nut would be better, I did not pay too much attention to matching the length to the original one, this means that the nut is too wide to sit on the un-threaded part of the screw that stops the top slide from hitting the carriage under power. So a little more work needed there.

The new nut is such a good match to the screw profile that it feels tight as it rubs on the un-threaded part of the screw, which the old one didn't.

I need to make another nut to fit my turret slide, which I use with my milling attachment, I think I may open up the hole in the slide to allow me to make a bigger  nut spigot for added strength.

Bernard


----------



## robinj66

Hi Bernard - nice to see the idea in action:thumbsup:

So I can order the correct stuff, how thick was your acetal sheet to begin with(I don't want to dismantle my cross feed until I have the sheet in my clutches).

Robin


----------



## Dranreb

robinj66 said:


> Hi Bernard - nice to see the idea in action:thumbsup:
> 
> So I can order the correct stuff, how thick was your acetal sheet to begin with(I don't want to dismantle my cross feed until I have the sheet in my clutches).
> 
> Robin



Hi Robin, i ordered 22mm thick for pulley making, but 22.5 arrived, they must've been out of stock or summat, the extra is thickness useful because it gives some leeway when melting..

Off topic, but remember me saying Atlas lathes don't like               tungsten carbide tools? Well now I've got it all nice and tight, I reground a tc tool and now it cuts really well, and fast, no chatter till I pushed the cut to  .110 on CRS so not bad after all.

Be sure to keep us updated..

Bernard


----------



## Dranreb

Forgot to mention the headache free way to arrive at the cut line for the spigot end is to put the old and new nuts together on the screw, and scribe. Accuracy  is quite important to avoid binding in the nut as it nears the front, so best to sneak up on it...

Bernard


----------



## robinj66

Excellent - thanks for the tip


----------



## Splat

*Here's* another one.


----------



## Dranreb

Splat said:


> *Here's* another one.



Thanks Splat, hadn't seen that one.

 I have some 3/4" Acetate rod that I could have used to do a similar job as shown there, but with my worn nut I thought would have had trouble milling the housing part, also there is not much room for one in the Atlas carriage.

The more I think about it, I reckon a stepped spigot (so that the original type screw head could be used) and corresponding modified hole in the cross slide would be a worthwhile improvement for long term strength, summat like this. .  




I will be trying this when i make the one for my turret slide..

Bernard


----------



## iron man

How does the delrin hold up over time?? Oil tends to break down some plastic's and make it soft over time as well I would be curious to see how long it works out but I guess it would be easy to make a new one too. You could also make an acme tap I made one for brass going into plastic would be a breeze.. Ray

http://www.hobby-machinist.com/showthread.php/11924-Atlas-modifications


----------



## Dranreb

iron man said:


> How does the delrin hold up over time?? Oil tends to break down some plastic's and make it soft over time as well I would be curious to see how long it works out but I guess it would be easy to make a new one too. You could also make an acme tap I made one for brass going into plastic would be a breeze.. Ray
> 
> http://www.hobby-machinist.com/showthread.php/11924-Atlas-modifications



Some info here Ray             http://www.dynalabcorp.com/technical_info_acetal.asp

Bernard


----------



## Splat

I was going to say that I know Delrin/Acetal is used for gears and bushings, pulleys, and many other uses so I would imagine it's quite impervious to oils. BTW, thanks for the link Bernard.


----------



## iron man

Well if it stands up to the pounding it may just be a great thing keep us informed about how fast it wears in and how many hours before you get back lash.. Ray


----------



## Dranreb

Ray, I just remembered when I worked on construction machinery in the around 1972, we had 360 excavators and dozers working on tidal sea defence work, their bottom track rollers were supported by sealed roller/ball bearings that lasted no time at all. When they broke up the roller and pin was usually wrecked too, causing way to much down time, the tides determined the overtime we worked.

One day a chap came into the workshop with some large black plastic tubes and plain steel pins, which he wanted us to try out in the track rollers. How we laughed!:rofl:

Guess what? they lasted ages and ages, Can't remember if the pins where stainless or not, but the plastic never showed any noticeable wear and the pins wore instead, only the pins were replaced, and not till over half their thickness had gone. If grit did get embedded in the plastic it didn't show.

I left that job (loved the work, but rubbish hours/money) so don't know the outcome, but I now reckon that was Acetal/Delrin .

Bernard


----------



## iron man

Dranreb said:


> Ray, I just remembered when I worked on construction machinery in the around 1972, we had 360 excavators and dozers working on tidal sea defence work, their bottom track rollers were supported by sealed roller/ball bearings that lasted no time at all. When they broke up the roller and pin was usually wrecked too, causing way to much down time, the tides determined the overtime we worked.
> 
> One day a chap came into the workshop with some large black plastic tubes and plain steel pins, which he wanted us to try out in the track rollers. How we laughed!:rofl:
> 
> Guess what? they lasted ages and ages, Can't remember if the pins where stainless or not, but the plastic never showed any noticeable wear and the pins wore instead, only the pins were replaced, and not till over half their thickness had gone. If grit did get embedded in the plastic it didn't show.
> 
> I left that job (loved the work, but rubbish hours/money) so don't know the outcome, but I now reckon that was Acetal/Delrin .
> 
> Bernard



 I have seen that too in constuction equipment we use to make bushings out of nylon or teflon the pins would wear out before the plastic most of the time it was because the plastic would hold in the grit and sand it would become imbedded in the plastic and would basically grind the steel shaft down.. Ray


----------



## Dranreb

iron man said:


> I have seen that too in constuction equipment we use to make bushings out of nylon or teflon the pins would wear out before the plastic most of the time it was because the plastic would hold in the grit and sand it would become imbedded in the plastic and would basically grind the steel shaft down.. Ray



Reckon you're right Ray, I'll be keeping an eye on those pesky chips!

Bernard


----------



## iron man

Dranreb said:


> Reckon you're right Ray, I'll be keeping an eye on those pesky chips!
> 
> Bernard



 Keep us updated if this works there maybe other use's for this. Thanks Ray


----------



## cbtrek

Looks like I better order some material and try it.

Good Idea!


----------



## Dranreb

iron man said:


> Keep us updated if this works there maybe other use's for this. Thanks Ray



Well it's been a while and I've given it a fair pounding in that time.

After a bit, seemed that a little wear was taking place, but on inspection it appeared to me that the Acetal was changing shape, as the slot was wider than it had been.

I tightened the screws which achieved zero backlash again, but today I noticed that some backlash has re-appeared...

I think I have kept chips out of it, but some of them pesky things may have sneaked in somehow,

Re tightening the screws until the gap was closed reduced the backlash, but not entirely, so sadly I have to own up and declare this particular design a failure as a long term fix..

I think it must be my way of making a pastic nut, as I haven't read of any other designs failing.

Did anyone else try making one? If so how did yours last?

Bernard


----------



## 8ntsane

Hi Bernard
I have read so many success storys with delrin nuts, I wonder what is different with yours.
Seems you did a good job making the nut. Maybe the problem is else where. I have read the original thread from Evan. He did say he spent some time prepping the screw to ensure the burs were removed, and he also polished the screw. I have to wonder if you did that, and maybe you need to do a very close inspection of your screw to see if it could be the problem. Also, did you run the screw and nut dry? or was a lube of some sort used? There was talk of using different things in the original thread. I don't know if it extended the life of the nut , or not. There was also talk of different types of delrin. Was the correct type used? Just wondering what went wrong. Could it be the materials, screw prep, lube, or no lube? Seems you did a fine job making the nut.
Hope you find out why your getting the wear. Let us know what you find.


----------



## Dranreb

Thanks for interest Paul, I think the plastic has to be enclosed in a metal housing somehow, as others have done, there may be some flexing going on, maybe the spigot has worn or is flexing a little as well, I'll have to check that.

It is known that these plastics can 'settle down' after machining, causing problems with achieving very accurate dimensions. 

As the nut was not a full circle, and heat was used I think it has moved a bit like wood drying out. Milling with the cross slide gibs pretty snug may have put extra strain on the nut and forced it apart.

It was OK dry, but a little lube made it very smooth, I only lubed it once.

The difference having zero backlash made to the lathe was amazing, especially when milling, I've picked up a few quality NOS end and 2 flute cutters cheap and was able to mill better than I ever hoped with my little Atlas.

Hey ho...back to the thinking chair (I Don't have a drawing board) 

Bernard


----------



## iron man

I dont think I would give up as of yet. I would try making a tap out of an old piece of acme threaded rod and tap it instead of heat forming it. I know that plastic when heated lose's its oils and will change shape and can get brittle over time. If that is not it maybe enclose it in a metal shell. Or maybe another plastic such as *Turcite...* Ray


----------



## Dranreb

No I haven't given up yet iroman, just giving it more thought, I do lean towards the impetuous sometimes...

Bernard


----------



## 8ntsane

Looking at the pics again, I wonder if the screws that you say are self tapping are maybe the problem?
Meaning the plastic they thread into is being pulled out of shape some. Do you have room to change them
to a nut and bolt arrangement? , with possibly a nyloc nut? I was thinking there must be a fair bit of force
to close the gap when adjusting back lash. If you have room, it could provide a better clamping force. Just a thought.

You also mention lube helped. If I recall that thread Evan started, there was talk of coating the screw threads
with graphite, and I think other talked about wrapping the screw with Teflon tape befor the heating process.
I don't know who tried what, but the thought was to impregnate the delrin with what ever was used. That just come to mind when IronMan mentioned the material losing the oils from heating, and drying out some.


----------

