[clocksandblocks]

Hey every one, this is probably a redundant thread and I'm sorry but I tried to search for answers to my problem with no avail. I just finished building my first CNC router using Ebay (I know I know!) ballscrews. Its just for playing around in the garage so I figured these would be fine.

Well after getting everything set up and the machine cutting out parts I noticed they are all coming out undersized. When I tell it to cut out a 2" circle, the circle actually comes out to be 1.915 in diameter. The ballscrews I bought are metric (16mm in diameter) From Ebay seller "Linearmotionbearings2008" Who sells TONS of these ballscrews there. I was skeptical when I was told they have a thread pitch of 5 turns per inch because if they are metric in diameter I would assume the pitch is metric as well. after cutting a few parts out I can say for sure they are NOT 5tpi...

Is there a way to calculate the tpi on these ballscrews now that the machine is up and running? Or does any one know the real TPI on these ballscrews? Thanks for any help! I have attached a picture of my homemade CNC router I built that is cutting the undersized parts.

-Jerome

[tulsaturbo]

You need to set your motors SPI (steps per inch). If you are using Mach3, its a simple procedure. Below is a video that should help:

[ame="http://www.youtube.com/watch?v=OTHdgk12EcI"]YouTube- Mach 3 Steps Calibration[/ame]

[mactec54]

clocksandblocks
He probably ment 5mm, 5 turns per inch would be .200 per turn
5mm pitch would be .19685029 per turn enough to make your parts cut small But you can set it up as tulsaturbo has already said in the above post

[clocksandblocks]

Thanks for the info guys. I use EMC2, is there an easy way to do this calibration in that software as well?

-Jerome

[Andre' B]

Lay a ruler up to the ball screw and see how well the 5mm marks line up with the thread.

If it looks good use mactec54's number of 0.19685029 inches per turn.

Divide your steps per turn by the inches per turn and you get steps per inch.

Assuming you are using 10x micro stepping drivers.
200 step per turn motors x 10 micro steps = 2000 steps per turn

2000 / 0.19685029 = 10160.005 steps per inch.

[mactec54]

clocksandblocks

How did you do it to get the 5 turns per inch that you have now, if that is what you have entered, then just change it to 5.08000000002 & that will make it for 5mm pitch
You most likely don't need all the zero's on the end

[clocksandblocks]

I asked the Ebay seller I bought the ballscrews from what the pitch was and he said 5tpi. He isn't returning my emails now so I will try changing the numbers to the metric pitch, that sounds like it should do the trick.

[kawazuki]

I asked the Ebay seller I bought the ballscrews from what the pitch was and he said 5tpi. He isn't returning my emails now so I will try changing the numbers to the metric pitch, that sounds like it should do the trick.

If he's saying its a 5tpi screw then it possibly measures 15.875mm dia or 5/8" imperial which would tie up? Even if it is a metric 5mm pitch the conversion doesn't tie in with your stated undercut? So maybe there is some lash in the set-up that also needs addressing?

Mactec54 - then just change it to 5.08000000002 & that will make it for 5mm pitch. You most likely don't need all the zero's on the end

How did you arrive at the 0002 at the end? 25.4mm / 5 = 5.08!

[mactec54]

kawazuki

5mm is .1968503937 divide that x 1.00 will give you 5.08000000002 if you read the post you would of seen that I said he did not need all the zero's on the end so he would of put in 5.08, His screw is 16mm not 5/8 dia

He had it set up for .200 this would make it cut undersize when it should of been for .196850

[mactec54]

clocksandblocks

Is the part number for your ballscrew RM1605 or RM1610 this tells you the dia & the pitch

[kawazuki]

kawazuki

5mm is .1968503937 divide that x 1.00 will give you 5.08000000002 if you read the post you would of seen that I said he did not need all the zero's on the end so he would of put in 5.08, His screw is 16mm not 5/8 dia

He had it set up for .200 this would make it cut undersize when it should of been for .196850

Just because someone says its 16mm doesn't mean it is 16mm - not when the seller says its 5tpi. Could you visually tell the difference between 16mm and 15.875mm?

Anyway why set the machine up with metric screws and talk in inches? Set it as metric - each unit is 1mm, the screw moves the object 5mm for every rotation? For every 1mm the screw rotates 0.2 of a turn or 10 steps. Use a
G20 or G21 in code if you prefer working in imperial or native units, the converse obviously applies if the screw actually is imperial!

Anyway - all the above rambling doesn't add up to 1.915" as opposed to 2"

[mactec54]

kawazuki

You only need to go to Ebay & look at what the screws are it tells you they are metric, I think clocksandblocks just has some setting up to do to get it right

[gmfoster]

Hey every one, this is probably a redundant thread and I'm sorry but I tried to search for answers to my problem with no avail. I just finished building my first CNC router using Ebay (I know I know!) ballscrews. Its just for playing around in the garage so I figured these would be fine.

Well after getting everything set up and the machine cutting out parts I noticed they are all coming out undersized. When I tell it to cut out a 2" circle, the circle actually comes out to be 1.915 in diameter. The ballscrews I bought are metric (16mm in diameter) From Ebay seller "Linearmotionbearings2008" Who sells TONS of these ballscrews there. I was skeptical when I was told they have a thread pitch of 5 turns per inch because if they are metric in diameter I would assume the pitch is metric as well. after cutting a few parts out I can say for sure they are NOT 5tpi...

Is there a way to calculate the tpi on these ballscrews now that the machine is up and running? Or does any one know the real TPI on these ballscrews? Thanks for any help! I have attached a picture of my homemade CNC router I built that is cutting the undersized parts.

-Jerome

Jerome

There are several ways to get your actual TPI or metric pitch of these screws depending on which they really are.

The easiest is to just measure the pitch. Count the threads over 1 in or any other convenient distance with a caliper.

If that doesn't come out to some integer then they are probably metric and the pitch is even easier to check with a caliper.


Actually you can get real close with just a machinist ruler.


If that doesn't work for you then move (in one axis only) a certain number of steps and measure that. To set steps you should start simple and a circle is not that simple.

Straight lines first then on to ortho shapes and after you get that working on to more complex shapes. If you notice the calibration video some one posted they are doing one axis at a time and its really easy to work out.

And yes the set up in EMC is very similar to what is shown in Mach.. You set it up initially. Just go back and edit..

But the real point is do one thing at a time if you want easy...Other ways will work but why not keep it simple.

All it takes is put a pen in your router set x to 0 and then g0 x10 in MDI and see how far it moves. Once you get your X you can copy to any other screw that matches and you will be real close. On to calibration for lead error. Any time you do this always move in the same direction. If you go back go to g0 x-1 then G0 x0 so you are not confusing backlash or timing issues with lead.


Now that you have the TPI set accurate you can go back and forth (in one axis) and see if that step and direction function with out timing issues causing losses on reversal.

Garry

[mactec54]

gmfoster

It's not that easy to measure a 5tpi ballscrew (.200) & a 5mm ballscrew (.1968) there is only .003 difference in pitch between the 2 ballscrews a dial indicator is realy the only way to set it up correctly, to be able to measure this ( a machinist Ruler I don't think so the lines on the ruler are more than .003 thick)

The screws that he has are 5mm pitch, that is all the guy on Ebay sells is metric screws,these screws are a C7 which will have a lead error of .005 per 12" aproximate, He will have to take care of this in the turning/set up as well

[gmfoster]

gmfoster

It's not that easy to measure a 5tpi ballscrew (.200) & a 5mm ballscrew (.1968) there is only .003 difference in pitch between the 2 ballscrews a dial indicator is realy the only way to set it up correctly, to be able to measure this ( a machinist Ruler I don't think so the lines on the ruler are more than .003 thick)

The screws that he has are 5mm pitch, that is all the guy on Ebay sells is metric screws,these screws are a C7 which will have a lead error of .005 per 12" aproximate, He will have to take care of this in the turning/set up as well

sure it is .oo3 over 10 is .o3 and if you can't measure .o3 something is wrong.

Lets see .2 over 10 threads is 2 inches where .1968 over 10 threads is 1.968 inches so that's .032. that's over 2 inches. If you can't see .032 in 2 inches you have real trouble. But he is seeing .08 over 2 inches in his parts.

Oh and if you can't see .o32 over 2 inches then the the normal machinist rule is 6 inches.

.2 x 30 threads is 6 inches I believe.
.1968 x 30 threads is 5.904 and now all you have to see is .1 inch easily seen on a machinist ruler.

Plus there have been many other methods shown.


In addition there is the fact that he states he us off .085 over 2 inches. which doesn't work out to either one..
So again.
What I never understand is why hardly no one ever starts out getting linear things working first.
Garry

[mactec54]

gmfoster

If you read the posts, clocksandblocks knows what he has to do to get it right, He does not need a machinist ruler, he could do it with a tape measure

I'm new you would get excited about you machinist ruler! common sense rules

[gmfoster]

gmfoster

If you read the posts, clocksandblocks knows what he has to do to get it right, He does not need a machinist ruler, he could do it with a tape measure

I'm new you would get excited about you machinist ruler! common sense rules

First you say it tough and can only be done with a dial indicator now you say it can be done with a tape measure.. Where is this common sense..
I read the thread.. You said

gmfoster

It's not that easy to measure a 5tpi ballscrew (.200) & a 5mm ballscrew (.1968) there is only .003 difference in pitch between the 2 ballscrews a dial indicator is realy the only way to set it up correctly, to be able to measure this ( a machinist Ruler I don't think so the lines on the ruler are more than .003 thick)

The screws that he has are 5mm pitch, that is all the guy on Ebay sells is metric screws,these screws are a C7 which will have a lead error of .005 per 12" aproximate, He will have to take care of this in the turning/set up as well
________________
Mactec54

You said its tough to determine.
I said it is very easy.

I am not excited about the ruler.

If you read the thread you would see that the inch metric offset shouldn't cause the error he is getting all by itself.

[keebler303]

No one has even said anything about the size of the cutter! Most cheap ones are off by several thousandths. That combined with the metric/imperial error could be significant. You all are also assuming that he is measuring the bore properly. How was it measured?

Matt

[packrat]

Also what was the tool offset he(O/P) was using?

[mactec54]

gmfoster

clocksandblocks first has to set up the machine, then look for other things, like tool dia, tool offsets, Etc, He has built a nice machine so I'm sure he will get it right.

gmfoster
The only way to set his machine up is with a dial indicator, to measure the ballscrew if he measure's over 2" LIKE YOU SAID it would be .032 then he can use a tape measure, But he does not have to measure the ballscrew now, because he knows now that it is 5mm pitch

gmfoster
If you have a better way to set up the machine without a dial indicator then every one here would like to know how?? (May be it's that magic machinist ruler you are talking about)