[bladehunter]

Just starting to throw some ideas for my X axis out there. Idea is to use a 1204 screw & nut (now that Chai has 'em), for now have the ballnut bracket on standoffs but will be eventually mounted to the end of a longer top slide. After reading some notes in MEW regarding a ML7 conversion I'm going to try out a nema17 motor with a 2:1 reduction.....Everything is designed to be modular so if I need a change of motor all that is needed is a new motor plate and a longer belt. Compound will be removed and I will use a solid tool post as I am using now.

Here are some ideas drawn in sketchup. Any suggestions would be appreciated.

Attachment 202910

[pippin88]

I've converted one of those lathes: http://7xcnc.com/hardware/my-conversion/

I used 1/2" acme. It works ok, but there are some inaccuracies that I feel relate to my screws and nuts. I machined them manually and didn't get the journals concentric. Diy acme nut ain't great either.
It's a very small area in the cross slide and I often wish I'd gone a model up, mainly because of this issue.
I've seen someone use an 8mm ballscrew but they are quite expensive. Avoidable at zapp automation in UK.
I'm also considering making a new cross slide, with grid of holes for gang tooling perhaps. Downside would be loss of swing over the slide

[bladehunter]

Hi Pippin

I've seen your conversion in the last week or so, kinda what gave me the kick to do mine. When all is said and done the loss over the X slide isn't such a big loss, getting close to what you can swing over the X-slide is pushing the limits.

I had a look at the 8mm ballscrews but my lead screw is offset in the cavity in the saddle, no enough meat to machine the cavity to fit the nut. Hence the reason the ballnut is mounted out back.

One of the best mods I made to my Titan, along with taper roller bearings and ditching the compound slide, was installing thrust bearings either side of the RH bearing block, for manual use anyways. That's the reason for the x axis bearing I'm using a bronze bushing with thrust bearings either side.
A new X-slide is on my list as well, tossing up whether to go with laminated construction or machine from hot rolled steel or cast iron if I can find some at a reasonable price in Sydney, issue 144 of Model Engineers Workshop has an article regarding machining a new X-slide from cast iron ( I have a spare copy if you're interested).

[pippin88]

Another option is to have the ballscrew beside the cross slide (on the tail stock side).

If you have space at the back of the machine, then you don't really lose anything much by doing what you have planned. Force is in the direction of the standoffs (I'd use a solid block if possible) so should be good.

My dodgy delrin ACME nut is mounted to the back of my cross slide (rather than under the middle like the original brass nut).

I'm still try to decide how to re-do mine.

[dick cnc]

Here is my 7 x 10 I don't have a lot of pictures not is mounted behind the cross slide 16mm screw

[bladehunter]

Had a another play around today and came up with a side mount for the X axis. Comes out about 10mm further at the front than last design but doesn't sit out at the back and the ballscrew is only 200mm long including machined end. Loss of travel due to the mount is about 45mm which is more or less what a drill chuck or live centre takes up when mounted in the tailstock. Tho I did have to incease the pulley centres to allow for the thicker aluminium mounts. The first was going to made from BMS.

Only 4 parts to machine, bearngs & motor bracket are now one piece. Everything mounts via 2 bolts where the apron normally bolts in, not drilling required to the cross slide, bracket for the mount is sandwhiched between the cross slide and the tool post.

Attachment 203254

[pippin88]

I look forward to seeing your results.

That design would lend itself well to a new cross slide later, with provision for gang tooling.

Consider asking Chai to cut down the ballnut flange. From what I can find, the 1204 nut will be 32 high (flats of flange), but should be able to be cut down to ~22 (the diameter of the body of the nut)

Another option is trapezoidal (metric acme) screws.
Pretty cheap: http://www.ebay.com.au/itm/TRPZ10x2-...item43b8c33770
Though for some reason the nuts aren't showing up in their store at present.

[bladehunter]

This is the info Chai gives for his 1204 nut, seems like a compact little unit. That's the one I've based my design on.

Attachment 203262

[bladehunter]

OK it's been a while but I've managed to completely do something different to my plans, well some what.



Inverted view. Nut stays put, bearing & motor move with X axis.





I hope this gives an idea of what I'm doing. Yes that's a NEMA 17 stepper. Tony Jeffree tested a slightly lower rated NEMA 17 on a Myford conversion with the standard screw and was pleasntly suprised with how it went. I'll be using a 2:1 reduction. Still some work to do to get it dialed in, but before that I'll be working on the Z axis now that all the ball screw & bearing blocks have arrived. I also managed to make a fly cutter (without access to a lathe) so hopefully surface finish will improve.

[pippin88]

Interesting strategy, could work really well. Had not thought of doing that. What travel are you getting?

I presume you had to mill the saddle somewhat.
Got any photos with just the screw?

If you add bracing on the sides it will be a lot stiffer

Can you confirm the dimensions of the 1204 nut?

[bladehunter]

I think I designed for 75 - 80mm travel.

I had to bore the hole where the screw goes through in the saddle out to 17mm for the ballnut to fit, that was all that was needed.

I really haven't given any thought to adding any bracing. The section of plate where the bearing block\motorplate mounts is about 5.5mm thick, the block itself is 50x23 wide and is fixed by 2x20mm M5 cap screws. I thinking that should by stiff enough. Then again I wont know til it's under load.
Ideally I'd like to machine a new cross slide out of CI (as MEW issue 208) with a neater mount for the motor\bearing block.

This is the same model of THK ballscrew\nut\bearing I bought.

Attachment 222502

[lcvette]

How did this end up working for you? Very cool idea!

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