Project of the Month built by SilverSanJuan
Home Model Engine Machinist > CNC and 3-D Printers > CNC Machines and Conversions > How to combat crabbing

Reply
 
Thread Tools
Old 02-10-2015, 09:47 AM   #21
///
Simon
 
Join Date: Sep 2011
Location: Perf, Straya
Posts: 468
Liked 67 Times on 60 Posts
Likes Given: 28

Default

Thanks for the warning John, I have read many similar tales of woe regarding round column mills.
There do seem to be some devotee's of them, though I don't understand why.

Fortunately, the '45' model RF does have a square column, I believe it is the only one.
Unfortunately, the range of RF45 clones here in Australia is pretty thin compared to other countries, I have found only this one: http://www.machineryhouse.com.au/M123
It appears to be very slightly smaller than those available overseas(comparison chart here: http://www.hossmachine.info/rf-45_clone.html)

However, when compared to the only other locally available option in a similar size/price class (the SX3) it is far more appealing.
Whenever I visit that store I have a play with it and the SX3 that sits right next to it.

Photo below was pinched from fignoggle, comparison of the Rf45, the X3 and X2. There's a bit of foreshortening going on in the photo making the Sieg machines look smaller, but it is still a chunky machine.

Nice workshop you have there. I have about half the space shown in that photo. Want to swap?


Attached Thumbnails
figNoggle_x2x3rf45Perspecti.jpg  
__________________
"The reality is that without cheap imported machines, I would be spending my time doing something less creative and less enjoyable" - Captain Jerry

Last edited by ///; 02-10-2015 at 09:59 AM.
/// is offline  
 
Reply With Quote
Old 02-10-2015, 11:20 AM   #22
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,432
Liked 605 Times on 456 Posts
Likes Given: 53

Default

Misunderstanding by me, I never knew the RF machines came in other column designs.
That isn't now my shop, it has been upgraded a little since then.

John


Blogwitch is offline  
 
Reply With Quote
Old 02-10-2015, 12:29 PM   #23
Cogsy
 
Cogsy's Avatar
 
Join Date: Jul 2012
Location: Perth, Western Australia
Posts: 1,608
Liked 416 Times on 318 Posts
Likes Given: 373

Default

Quote:
Originally Posted by /// View Post
However, when compared to the only other locally available option in a similar size/price class (the SX3) it is far more appealing.

Sorry to hijack your thread John, but a caution for Simon - I have the previous version of the one you linked, the HM-45 from Hare and Forbes. A quick look at the specs and the only difference I can see is the digital tilting angle guage. Mine is a late 2009 build and it's terrible.

The biggest bugbear is the feed on the Z axis. It's a simple rack cut into the quill itself, with a drive gear that is not ajustable for backlash and has a ton of it. So as you lower the quill it moves fine (dropping under it's own weight), but if you load the cutter and feed down the backlash comes into play. The quill can stop moving and then suddenly drop 2mm (yes 2 whole millimetres) instantly. It can be a huge pain when plunge cutting to depth.

I got mine secondhand from a deceased estate so I had no warranty or comeback on it, but had I known about the issue I might not have bought it at all (even though it was cheap).

Now I'll shut up and let the thread get back on topic.
__________________
Al.
______________________
I'd like to be a perfectionist, but I lack the patience...not to mention the skill...
Cogsy is offline  
 
Reply With Quote
Old 02-10-2015, 01:02 PM   #24
///
Simon
 
Join Date: Sep 2011
Location: Perf, Straya
Posts: 468
Liked 67 Times on 60 Posts
Likes Given: 28

Default

Thanks Al. I've played with the demo model many times and the quill felt nice and smooth, but obviously I've never used it under load. Damn
Yes, back to the regular programming, apologies John.
__________________
"The reality is that without cheap imported machines, I would be spending my time doing something less creative and less enjoyable" - Captain Jerry
/// is offline  
 
Reply With Quote
Old 02-12-2015, 12:56 PM   #25
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,432
Liked 605 Times on 456 Posts
Likes Given: 53

Default

I know exactly what Cogsy is on about, and to test for it, slacken off the quill screw lock, and move the quill up and down a couple of times. Then with the machine off (obviously) try to lifting the quill up and down by hand on the quill nose. Usually you can easily feel that quill movement, and the only way to eradicate it is to put a strongish spring LIFTING the quill UP. Otherwise your Z axis can be almost anywhere.

John
Blogwitch is offline  
 
Reply With Quote
Old 02-12-2015, 05:27 PM   #26
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,432
Liked 605 Times on 456 Posts
Likes Given: 53

Default

Now getting back to the crabbing question.
Having given the mill a good dose of looking at and stripping a scrapper down at my friends house, to start the centre Z axis lift modification, it was rather easy to figure out.
If you remove the four screws holding the main motor and spindle block (plastic) and the motor will then swing 90 degs to the side. So having seen this done, it will allow masses of room to get the ball nut mounted behind it in the centre. The motor will require an L bracket underneath it for support, and while I am doing mine, I will up the gear ratio to give me another 50% in speed. 100% has been tried before, but it did lose a fair amount of power, but I think things should be ok at a 50% uprate as long as I don't go using big cutters.
Here are a couple of pictures to show what I mean. The coarse handle downfeed and the fine feed will both be removed as they are not required.

Motor swung to one side.



Where the ball nut will be fitted, the screw will go downwards, so not sticking up in the air.




John

Last edited by Blogwitch; 02-12-2015 at 05:30 PM.
Blogwitch is offline  
 
Reply With Quote
Old 02-12-2015, 06:06 PM   #27
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,432
Liked 605 Times on 456 Posts
Likes Given: 53

Default

Just to add a little to the above where I am considering uprating the speed.
I don't know if doing that will blow the normal circuit board, which I suspect it might. On the version of mill I have bought, Arc had the circuit board modified so that it shouldn't blow even if the quill came to a dead stop whilst in operation, it just shuts down, and as long as a power off / on is done, it should start up as normal. I suppose the special SX2 from LMS should have the same thing, as Arc share their findings with them, that is where the strengthened column comes from.
I will be doing a full post on making this machine, but it is now being held up by good quality parts from China which won't be here for at least another month, but I can give you a bit of insight into what has been bought from China, to give you some idea of the cost. I am hoping to make the complete machine and everything that goes with it for less than 1750. I have just bought a second hand 15" touch screen monitor off ebay for less than 80, and it is bomb proof, it could be kicked around the workshop floor and still display Mach 3, plus another litle gadget, a pendant controller for 4 axis Mach 3 was only just over 20. So things are moving slowly but surely, just how I like it.

Ball screws

http://www.ebay.co.uk/itm/160577603846

Stepper controllers

http://www.ebay.co.uk/itm/NEMA23-Ste...-/140749152634

Breakout board

http://www.ebay.co.uk/itm/2613958360...%3AMEBIDX%3AIT

Everything else is being sourced locally.

John
Blogwitch is offline  
 
Reply With Quote
Old 02-12-2015, 06:25 PM   #28
///
Simon
 
Join Date: Sep 2011
Location: Perf, Straya
Posts: 468
Liked 67 Times on 60 Posts
Likes Given: 28

Default

Ahhhh interesting.
It is even easier on the old original X2's (like mine) as there is enough room to fit the ball nut without moving the motor.
Looking forward to seeing more.
__________________
"The reality is that without cheap imported machines, I would be spending my time doing something less creative and less enjoyable" - Captain Jerry
/// is offline  
 
Reply With Quote
Old 02-12-2015, 06:36 PM   #29
///
Simon
 
Join Date: Sep 2011
Location: Perf, Straya
Posts: 468
Liked 67 Times on 60 Posts
Likes Given: 28

Default

I found it has been done before, tho with the original version.
Note the gap between motor mount and column, room galore.
Attached Thumbnails
X2-YZ-300.jpg  
__________________
"The reality is that without cheap imported machines, I would be spending my time doing something less creative and less enjoyable" - Captain Jerry
/// is offline  
 
Reply With Quote
Old 02-12-2015, 06:54 PM   #30
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,432
Liked 605 Times on 456 Posts
Likes Given: 53

Default

Simon,
We looked at it that way, but the size of ballscrew we want to use (a very strong 16mm) the nut just wouldn't fit in without hacking off almost all of it's support flange. That looks to be a much smaller screw.
Plus doing it in that position means you have to cut through all sorts of casting shapes. By taking it further forwards, you come into well supported and easy to machine areas.



Just our way of doing things, make it bombproof from day one and it shouldn't cause any problems later.
All we are after is a very rigid setup with zero backlash, and of course, no crabbing.

John



Last edited by Blogwitch; 02-12-2015 at 06:57 PM.
Blogwitch is offline  
 
Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Newest Threads






- Top - Member List