Need ballscrew advice please

[cnczoner]

Although I've investigated this a few times before, now the need is urgent. (I'm getting an odd finish with the stock acme screws on my mill and it seems to be narrowed down to bad lead screws, and since I planned to do this conversion anyway...).

So here are some basics...
- Mill is an HF 42827, (CNC converted by someone else). X and Y travels are just shy of 20" x 7".
- I want to convert just X and Y to ballscrews for now. (99% of my projects will be 2.5D).
- Current acme screws are 23mm dia with 17mm shafts. X is supported at both ends, and Y is supported at the front only.
- Mill has a 1.5hp spindle, and I am fine with my 30ipm rapids (it'll do 40ipm, but I keep it at 30 to prevent lost steps).
- 99% of my work will be 6061-T6 aluminum.
- I want to get the best finish possible straight from the milling operation.
- I need zero backlash, but accuracy is not a concern.


My thoughts so far...
- 15mm dia ballscrews should be fine, but if I get 19mm at a decent price, I'll probably bite. Going over 19mm is a major step in cost, because I'd have to get it machined elsewhere because my lathe has a 3/4" bore (just over 19mm).
- I want to use ground ballscrews with a single nut loaded with larger balls for zero backlash. (Double nuts will reduce the precious travels).
- C7 or worse is fine.
- I'm thinking I'd stick with 5mm or 10mm per turn.
- With the smaller-diameter ballscrews (than stock), I may need to provide rear support for the Y-axis as well.

To this end, I was looking at Roton ballscrews, but they're apparently rolled and according to a tech, they can't be loaded to get zero backlash. McMaster wants an arm and leg for their mystery-brand ballscrews, so I'm looking on Ebay. Most of the good name brands will run me in the $1k range, and I'm unsure about Nook (which I've heard is odd because it makes crunching noises).

I found some decent used candidates (Kuroda, THK, etc) but they're about ~$200 per axis, so I'm still looking. For the screws, nuts, angular contact and free-end radial bearings, I was hoping to come in within $300-$400, but if I have to stretch that for the perfect solution, I will.

Thoughts? Am I on track here?

Cheers,
-Neil.

[cnczoner]

BTW, here are some photos and dimensions of the mill. The filenames explain each image...

Mill_Acme_01_X_Right_End.jpg
Mill_Acme_02_X_Left_End.jpg
Mill_Acme_03_Left_Bearing_Block.jpg
Mill_Acme_04_Left_Bearing_Block_Inside.jpg
Mill_Acme_05_X_Shaft_Left.jpg
Mill_Acme_06_X_Shaft_Left.jpg
Mill_Acme_07_X_Shaft_Left.jpg
Mill_Acme_08_X_Shaft_Left.jpg
Mill_Acme_09_X_Shaft_Underside.jpg
Mill_Acme_10_X_Shaft_Right_Mount.jpg
Mill_Acme_11_X_Shaft_Left_Underside.jpg
Mill_Acme_12_X_Shaft_Left_Underside.jpg
Mill_Acme_13_X_Shaft_Left_Underside.jpg
Mill_Acme_14_Y_Front_Saddle.jpg
Mill_Acme_15_Y_Rear.jpg
Mill_Acme_16_Y_Rear.jpg
Mill_Acme_17_Y_Rear.jpg
Mill_Acme_18_Dimensions.jpg

[mrcodewiz]

I am converting an X2 using the roton 5/8 screw. They packed the nuts with larger balls to reduce the backlash for a fee - I will let you know how much it was 'reduced' once it is together. I am hoping that the travel on the X2 is short enough that it will minimize the inherent accuracy of the rolled screw.

[Oldmanandhistoy]

Hi,
Have you seen here http://www.homeshopcnc.com/page12.html I bought mine there.

John

[cnczoner]

Roton said they'd get it to a few thou of backlash. The price is right, but not if the product is not exactly what I need.

I did find homeshopcnc, and I like that they can machine the ends. But for two axes the screws alone add up to ~$520. If I use their endblocks, that adds another $350, so I'm up to about $900 shipped. It's zero backlash, but C7. Sure I don't need better than that, but I think it's on the pricey side. I could make my own endblocks, then I'd be in the $650 range, so I have that bookmarked.

From ebay, I think I can get a full solution in the $450-500 range. And I found another person on ebay who sells and rebuilds ballscrews and says he can machine the ends. If that works out pricewise, I think it may be the best option.

Just keeping all my options open.

But in the meanwhile, anyone have thoughts on my screw sizing?

Cheers,
-Neil.

[justinm7]

You can get the journels on you existing screw chromed and than i would order a replacement Acne nut and put it on your existing screw
Justin

[timlkallam]

Neil I sent you a private message .

[SORCHEROR]

why not buy two non preloaded nuts for each screw,and use the second nut to dial out the backlash,thats what i did with my x2 using nook ball screws,two non preloaded nuts cost me about 20 bucks more than one preloaded nut,using two i was able to get almost zero backlash,about 4-6 tenths average per axis,i would use nook for the screws

[Eurisko]

Hi Neil,

I'm going to give Nook a try.

Just ordered a 5/8 dia, 48 in. ballscrew with two single circuit ballnuts.

The total price was $126.59 (excluding shipping).

The ballnut flanges are waaay overpriced, I'll have to make my own.

Lead accuracy is +-.004 per foot. Maybe screw mapping software can help with that.

http://www.reidsupply.com/detail.asp...ok%20ballscrew

[cnczoner]

Justin, I'm not familiar with chroming thing, but I wouldn't order the same acme nut from the same source (HF). If I can find an aftermarket source for the same size acme nut, but with higher quality, then I'd be interested. But are you suggesting that this chroming thing would correct any problem that would exist with the acme screw? And can acme screws realistically get to zero backlash?

Sorcheror, dual preloaded nuts would be great, but would take away a significant amount of precious X-travel. With some saddle grinding I may be able to use this for the Y-axis though.

Eurisko, that actually sounds good, but a general question for the Nook users -- do they actually make a crunching sound, or is that just one user's experience (that I read) who may have had an odd problem with his?

Tim, I'll check my PM.

[lgalla]

Neil,
I have read about the crunching sound of the Nooks.It was on the Homeshop Q&A when they had Nook's.It had to do with when they preloaded the nuts.Apparently ballnuts on rolled screws should not be loaded with oversized balls.This makes the crunching sound as the rolled lead accuracy is too low for oversized balls.This is why double nuts are used with rolled screws.
Larry

[skmetal7]

Crunching? nah, they are very smooth, even when preloaded. I have never handled a ground ballscrew so I cant compare it to them. When you preload the ballscrews, load a large ball then a standard .125" ball. This will keep the balls from running into eachother.

disclamer : I only have used nook ballscrews