PRT Alpha Help.

[jzarski1]

Well I just purchased a used 48x96 PRT alpha. It was kind of a gamble as there was no way for me to get power to it where it was. Well I am happy to say it works, but there are a few small issues I need some help on.

1. I surfaced the spoil today and noticed little ripples on the surface. Kind of looks like chatter. It's only on the X axis moves the Y axis is smooth as glass. The pinions look ok, this machine was used to cut foam only. So my question is what else could be causing this?

2. Is it normal for the motors to be so loud? Like a wining sound when they are moving. The motors are the direct drive ones.

3. One of the contractors is sticking. Does any one know what the model number and name is for the black and white contractors? Frank said they where replaced, but the replacement doesn't line up with the current holes. I was hoping to find the direct replacement. Didn't want to pull it out because then I won't be able to use the machine :D

Thanks for any help.

John

[jerry_stanek]

The ripples you see are because your spindle or router is not perfectly perpendicular to the table you should be able to get it plumb then those will be as good as your y

[Brady Watson]

Make sure the table is level or the X rails will have twist in them. Also, make sure it is cutting square by using the 3,4,5 method.

-B

[gene]

Pictures help so much more than words

[jzarski1]

The ripples you see are because your spindle or router is not perfectly perpendicular to the table you should be able to get it plumb then those will be as good as your y

I squared the spindle with my dial indicator. It's not the lines that you get when the spindle is out. It's actually tool marks on the table. At first i thought the cutter was nicked or broke. That checked out ok. I will goto shop later tonight and take a few pictures. I think it's chatter in the rack and pinion.

John

[ron_moorehead]

Here is a couple of photos on my contactors that were replaced a few years ago.

[jzarski1]

Here is a couple of photos on my contactors that were replaced a few years ago.

Mine look nothing like that. They have a white piece in the middle about an inch wide that goes in and out.

[Brady Watson]

Mine look nothing like that. They have a white piece in the middle about an inch wide that goes in and out.

Those are the old ones...prone to sticking. I've never had a problem, but I leave my control box on for months at a time...I never turn it off. My spindle isn't controlled thru it, so everything is inert when I close up for the night. SB sells replacements. They can be a bear to install without the right tools.

It is nearly impossible to gauge 'chatter' just surfacing the bed. If you have ridges in either X only or Y only, then your spindle is not perpendicular to the bed - dial indicator or not. Tramming never works right - the only thing that truly works is running the surfacing routine & reading the ridges.

When you've got your spindle dialed in properly, you should feel NO ridges ANYWHERE...however, a few thou is certainly in the ballpark and acceptable to most users.

I would put money on the pinions needing to be replaced. Foam or no foam, they are cheap and should be replaced and lubed properly. If they were cutting foam, chances are there was NO lube on X or Y because foam is attracted to grease and it gums up too easily. Racks are probably dry. If this is an Alpha with AS911 motors, then you absolutely 100% without a doubt need pinions. Those 20T ones don't have many teeth engaged in the rack and get hammered a LOT faster than the newer Alphas. Since it is a PRT, make 100&% sure that the X&Y turnbuckles are @ 3.5 turns out from just starting to barely pull on the spring. More or less - kills pinions.

Start there...

-B

[jzarski1]

Brady,

When you say 3.5 turns out from spring starting to pull out. Do you mean tighten the buckle and loosen it? Just want to confirm. I will order new pinions tomorrow for sure.

John

[Brady Watson]

When you hook the loose turnbuckle back onto the 3/8" stud/bolt, lightly turn it until it just starts to give resistance/the spring starts to tension/open up. Then 3.5 turns & lock down the nut with a 9/16" wrench.

-B

[tomwillis]

Brady - your info on the 3.5 turns helps me - too. Always wondered about that.
Thanks - Tom

[Brady Watson]

Tom,
Glad to help. The other thing to consider is that if they are too tight, they will wear out your rails prematurely.

-B

[jzarski1]

Here are some pics of what I am taking about. I know the straight lines that run the X axis are from the spindle being a tiny bit out. Looks worse then it is. You can barley feel those lines.

The issue I am taking about are what look like round tool marks. I am going to call it chatter. What is causing this

http://i576.photobucket.com/albums/ss210/jzarski/23%20Fish%20Nautique/2013-03-22_10-59-14_892.jpg
http://i576.photobucket.com/albums/ss210/jzarski/23%20Fish%20Nautique/2013-03-22_10-59-09_714.jpg


John

[Brady Watson]

OK...a few questions:

How did you generate the toolpath?


What program was used?
What diameter bit?
What was the stepover percentage or 'Overlap' value?
What was the move speed?
What RPM was it run?


-B

[jzarski1]

OK...a few questions:

How did you generate the toolpath?


What program was used?
What diameter bit?
What was the stepover percentage or 'Overlap' value?
What was the move speed?
What RPM was it run?


-B

I used the SB surface tool.
It was a 1" surfacing bit
Step over was 15%
Move speed was 6IPS
RPM.... Well that is kind of an unknown. The machine has a PC router but there is no dial to adjust the speed.

John

[gene]

Did you square the cutter in the x and y positions ? I know you said you used a dial indicator , did you dial it in at the 12 , 3 , 6 and 9 o'clock positions? It looks like its off in the y position

[jzarski1]

I am not so worried about the spindle being off a bit. It's the chatter marks on the actual surface that I am trying to eliminate. I only get the marks in the X (96") axis. The Y (48") axis is smooth as glass.

John

[Brady Watson]

Well, at first glance it appears that you are pushing the tool faster than the router can handle. I do not recall what default speed those single speed PCs run, but I would swap it out for a variable speed one. I would also check to see how secure the router is in it's ring & make sure that it is properly seated. There is a set screw & relief on the plastic liner that have to be clocked properly for the router to sit true to the mount.

In the meantime, if you have some scrap around, try the same bit & parameters at a slower speed and see if that makes a difference.

-B