Help with drill-Mill conversion

**Ross77** · 28-06-2009

How about using a Delrin nut instead of the brass(?) one (or a second nut made of delrin to remove backlash)

Cheers. The originals are cast iron, will the delrin be strong enough on their own if I replace them?

Wheres the best place to get ready made ones? as the thread is imperial (1/10 inch) Or is it still cheaper to buy a tap and make them my self?

**BillTodd** · 28-06-2009

I'd guess they'd be strong enough, although wear rate might be high.

I think one of the guys on the forum has been making and selling them (I don't know whether he has the correct tap for your threads)

What diameter are the lead-screws?

Are the nuts cast in place or are they removable?

Pictures would be good.

**Ross77** · 29-06-2009

Ok you'll have to excuse the photos and the state of my workshop. For some reason if i dont use the flash then there not in focus..:cry:

The screws are 16mm dia. (15.65 on the calipers) and have a 2.54mm lead (imperial 0.1") Cleaned and polished the screw so thats looking better but just noticed the nut has cracked where I have been tighting the pinch bolt, so definetly need a new one, ups.

The nut on the x axis is removable and the y axis is fixed.

Ive had a quick look on tinternet and found lots of different ideas but I'd like to know If any one has a tried and tested method, I've fitted bearings to the screw which was a major improvement, so just need to sort out the backlash in the nut..

Hopefully when its finished it should be a good MILL.....

**John S** · 29-06-2009

Screws are 5/8" x 10 tpi not metric,
Unfortunately 5/8" usually comes in 8 tpi.

Is it definitely an Acme screw or square thread, acme has tapered sides at 29 degrees ?

Then are they both RH, LH or one of each.

**BillTodd** · 01-07-2009

My question is how critical is it to completly eliminate backlash...

40 years ago men were sent to the moon. Most of the machines that built the rocket that got them there had backlash to some extent.

The critical bit is reducing the backlash/play/give/flex/strain/vibration/call-it-what-you-like it the whole machine down to workable level and working the machine to reduce the effect of the errors.

If you lock them together then wear becomes your problem. Spring them together with sufficient force to resist the tool pressure and you need monster size motors to turn 'em.

The important thing it to lock them together with the smallest possible clearance. This can mean that, with a poorly formed lead-screw thread, the nut will be slack in places while tight in others (lapping the thread with a nut and abrasive e.g. metal polish can reduce the tight spots).

**Ross77** · 01-07-2009

Thanks for all the advice, Taken it all on board. From looking on here and the CNC zone I always planed to use servo motors, linear rails and ballscrews for the main machine, and now I know why.....

Still all good practice, dont know If I can justify ballscrews for this one. No point in having an ultra precise table if the head flexs all over the place. May be I should just get it working and then if its just the backlash thats an issue, I can sort it then.

Made the tap tonight and tried it on some plastic I had kicking around. Worked fine but I think the plastic is to springy and the tap wont cut the last bit for clearance, very tight over a 40mm length. Ive tryed tapping fuild and a drill but the end result is a very hot and shiney leadscrew, Still at least I know the best way to polish them now :clap:. I'll have to order some delrin,or try narrower sections.

Changing the subject, what is the best way to hone the dove tails on the slides? I've got them really smooth, with no play, except for the the first 30mm or so where i can feel an bump, Cant get the oil stone in and dont want to over do it by using a grinder.....If I carry on lapping it will both parts wear and then cause problems over the whole length?

Thanks again

**Robin Hewitt** · 02-07-2009

Originally Posted by Ross77

Changing the subject, what is the best way to hone the dove tails on the slides? I've got them really smooth, with no play, except for the the first 30mm or so where i can feel an bump, Cant get the oil stone in and dont want to over do it by using a grinder.....If I carry on lapping it will both parts wear and then cause problems over the whole length?

If it is cast iron you scrape it, use engineers blue to find the high spots. I would be very careful about introducing any kind of abrasive unless you are blessed with a Rowlingesque magic wand, "Accio grit"

**Ross77** · 02-07-2009

Originally Posted by Robin Hewitt

If it is cast iron you scrape it, use engineers blue to find the high spots. I would be very careful about introducing any kind of abrasive unless you are blessed with a Rowlingesque magic wand, "Accio grit"

Cheers. whats the best tool to scrap it with? looked in to this when setting up the lathe but looked like a "Black Art

What is Accio grit? Im sure Ive read that it ok to use abrasive compounds as long as it is properly cleaned with parrifin afterwards...

**Robin Hewitt** · 02-07-2009

Originally Posted by Kip

Requires manual dexterity

The famous Mexican bandit :heehee:

**BillTodd** · 02-07-2009

You could try just lapping the parts together dry (i.e. degrease it and rub). Cast iron is fairly abrasive stuff so a few dozen cycles should polish the machining marks.

BTW Use proper 'way oil' e.g. Mobil vactra. (Keep that old can of Duckhams for the car use only ;) )