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728VT really unhappy!
- Thread starter 55fairlane
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This test was performed with an indicator (Brown and Sharpe. 0005 ) while traversing the head "up & down" , i.e. moving the Z axis negative then back again in positive....
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Can you please post a video of what you are finding? Im a bit confused about what you are seeing here, and by the PM you sent. That should clear things up for myself and all who are following along so we know we are focusing on the right thing.
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I'm not certain, I know I can email you a video, (I think) I'm a tool maker not a tech guy. But I will try tonight.
I will repeat the test trying to video it, but definitely getting still images.
Aaron
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I agree with @davidpbest that it is important that the spindle axis be parallel to the column on a square column mill. In addition, the quill, if equipped, (my Tormach CNC has only the column for z axis motion) has to be parallel to the spindle axis.
If a square is used, it must be a precision square. Verification of squareness is rather difficult without a precision square to use as a reference. Rather, I used a modification of the RDM method to determine parallelness of the spindle axis to the column. It should be done in both x and y direction. Mount a rigid bar known to be good regarding diameter and roundness in the spindle. I used an R8 collet for this purpose. Mount a test indicator so it contacts the bar near the collet when the quill is extended. rotate the spindle and note the minimum and maximum readings. Average the readings. Retract the spindle and repeat the rotation and readings. If the spindle is parallel to the quill, the averages will be the same. Do this in both x and y directions. It is unlikely that there will be a means for correcting any out of parallel situation but it is good to know if a it exists.
Repeat this process with the quill fixed in a retracted position, this time moving the column to determine parallelness between the spindle and the column. Correct any out of parallel situation by rotating or shimming the head. Once the spindle is parallel to the column, the usual procedure for tramming the head can be used but rather than rotating the head, the column would be shimmed to correct any non perpendicular situation between the spindle and the x and y ways.
One thing to note. The primary reason that tramming is done is to make sure the spindle axis is perpendicular to the ways so that successive passes don't result in cutting steps and the front and rear of the cutter contacts the surface equally. This test is really referencing the ways and if the table isn't parallel with the ways, using the top of the table as the surface trammed will result in an inaccurate tram. This also hold true if tramming to a vise or any other surface on the table. To work around this, before tramming, I mount a sacrificial surface to the table and skim the surface with a 1/4" end mill. the small diameter end mill will minimize any effect caused by an out of tram condition. This surface will be parallel to the x and y ways. Then tram using that surface in the usual fashion.
On another note, on a mill with a square collumn, the z axis gibs should be adjusted for minimum free play consistent with free movement. Excessive play will result in nod of the head due to its cantilevered weight. When making these tests, lock the quill and column before making measurements (not something I can do with my CNC mill, unfortunately).
If a square is used, it must be a precision square. Verification of squareness is rather difficult without a precision square to use as a reference. Rather, I used a modification of the RDM method to determine parallelness of the spindle axis to the column. It should be done in both x and y direction. Mount a rigid bar known to be good regarding diameter and roundness in the spindle. I used an R8 collet for this purpose. Mount a test indicator so it contacts the bar near the collet when the quill is extended. rotate the spindle and note the minimum and maximum readings. Average the readings. Retract the spindle and repeat the rotation and readings. If the spindle is parallel to the quill, the averages will be the same. Do this in both x and y directions. It is unlikely that there will be a means for correcting any out of parallel situation but it is good to know if a it exists.
Repeat this process with the quill fixed in a retracted position, this time moving the column to determine parallelness between the spindle and the column. Correct any out of parallel situation by rotating or shimming the head. Once the spindle is parallel to the column, the usual procedure for tramming the head can be used but rather than rotating the head, the column would be shimmed to correct any non perpendicular situation between the spindle and the x and y ways.
One thing to note. The primary reason that tramming is done is to make sure the spindle axis is perpendicular to the ways so that successive passes don't result in cutting steps and the front and rear of the cutter contacts the surface equally. This test is really referencing the ways and if the table isn't parallel with the ways, using the top of the table as the surface trammed will result in an inaccurate tram. This also hold true if tramming to a vise or any other surface on the table. To work around this, before tramming, I mount a sacrificial surface to the table and skim the surface with a 1/4" end mill. the small diameter end mill will minimize any effect caused by an out of tram condition. This surface will be parallel to the x and y ways. Then tram using that surface in the usual fashion.
On another note, on a mill with a square collumn, the z axis gibs should be adjusted for minimum free play consistent with free movement. Excessive play will result in nod of the head due to its cantilevered weight. When making these tests, lock the quill and column before making measurements (not something I can do with my CNC mill, unfortunately).
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I am not a tech guy either but what has worked for me in the past is taking a video with my cellphone and uploading it to Youtube. Everything can be done on the phone, no computer needed.
Sent from my iPhone using Tapatalk Pro
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@RJSakowski , your modified RDM is a good test well described. Would you please elaborate on what comprises a "rigid bar known to be good"? And provide some information on where to find one?
I also need to do this with my lathe.
I also need to do this with my lathe.
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Maybe I'm nit-picking, if so please forgive - but . . . If I take your explanation word-for-word, using this method you will know if the quill movement and the spindle axis are aligned. You do NOT know if the quill/spindle up/down movement is aligned with the head movement up/down. Assume for the moment that your "rigid bar" indicates zero TIR with the quill extended - you indicate to the bar, rotate the spindle, and see zero variation. Now retract the quill and repeat the same test and you get zero variation when the spindle is rotated. All you know is that the spindle/collet combination have zero TIR and that the spindle axis is parallel in both X and Y to the movement of the quill. You do NOT know if retracting the quill caused the "rigid bar" to move off the CL of it's original position unless you also look at how it was displaced. In order to know the quill/spindle combination move parallel to the head movement, you have to examine the displacement of the rigid bar in both X and Y, not just that the quill and spindle axis move parallel to each other.
Your method CAN measure that the quill/spindle movement agrees with the movement of the head up/down if you measure the displacement of the rigid bar with quill movement up/down - not just that the average of the rotational differences - and then compare that displacement to the displacement when the head is moved up/down.
The RDM method works fine on a lathe since you have only one axis being repositioned (the cross slide saddle moving along the ways). With a benchtop mill, there are two sliding elements (quill and head) that must conform to to parallel movement, which is why my personal preference is to use a machinist square or 2-4-6 block on the table as the reference surface to measure against. Even the inexpensive Chinese 2-4-6 blocks are sufficiently accurate to test quill and head conformity and to make the necessary adjustments to the column-to-base and head-to-column modifications.
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We spoke on the phone today, and as it seems to happen many times, a lot is lost in writing vs talking. Super nice guy as people almost always are. Anyway we may need some time with upcoming schedules, but we will get it worked out and will post an update once that happens. Didn't want to leave everybody hanging.
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- Dec 10, 2023
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I got my PM728VT last week and here are the results of my Z column and quill going up and down. .0005 DTI that i got today.
I am _not_ Quinn of Blondihacks that is for sure! I kick the tripod 3 times and say a few things wrong.
I am going to check tram and more tomorrow night. I know my tram is good as i used my old DTI and it is about one to two thousandth over the length my noga arm that holds the DTI (about 12inch diameter). I want to use my new DTI tomorrow to make sure it is good to great!
I am still learning so make sure you tell me if i am doing something wrong or if i can test better.
Any suggestions on fixing this 5 thousandths over the quill travel range of 3 inches let me know. I like Quinns method of only using the quill to set the depth of the cut. Do the major moves with the column. Then move the quill (less then one inch) to set the cut depth.
Can i live with approx 1.5-2 thousandths over 1 inch of travel? Now that i know it i will keep it in mind.
Thanks!
Chad
I am _not_ Quinn of Blondihacks that is for sure! I kick the tripod 3 times and say a few things wrong.
I am going to check tram and more tomorrow night. I know my tram is good as i used my old DTI and it is about one to two thousandth over the length my noga arm that holds the DTI (about 12inch diameter). I want to use my new DTI tomorrow to make sure it is good to great!
I am still learning so make sure you tell me if i am doing something wrong or if i can test better.
Any suggestions on fixing this 5 thousandths over the quill travel range of 3 inches let me know. I like Quinns method of only using the quill to set the depth of the cut. Do the major moves with the column. Then move the quill (less then one inch) to set the cut depth.
Can i live with approx 1.5-2 thousandths over 1 inch of travel? Now that i know it i will keep it in mind.
Thanks!
Chad
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