# PM25-MV saddle squareness



## Bluebutton (Apr 24, 2021)

I have had a PM25-MV mill for 3 years now and Just last month I finally had time to really use it.  The 3 year lapse was due to work and family issues.  The issue I am having is, if I indicate a 2/4/6 block to be trammed in in the X axis within .0005" across the 6" side of the block I find when I check the other edge of the block (4" side) I get a 0.010" run-out in the Y axis.  I have done this with a 1/2/3 block, angle plate and get the same results.  Also repeated the previous tests with the appropriate gibs locked and no improvement. The photos show that the Y axis non tapered dovetail is parallel to the reference surface on the surface plate, but when checking the X axis the same way its out 0.006".  I know this does not check squareness.  I did check squareness on the CMM at my work and it showed 0.004" out of square over 6 inches.   

I have searched the forums and found little info about the similar issues.   I have been in contact with Precision Mathews and they are helping me with the issue.  in the meantime im looking for all the info I can.  So far the only options I'm finding are to replace the saddle and gibs, or scrape the dovetails.  My question is has anyone experienced this issue and how did they correct it?


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## T Bredehoft (Apr 24, 2021)

You appear to be  reading on the dovetails. I'd prefer to read on a piece of stock, known square on the working surface of the machine, the table. That's where the work will be....unless I'm missing something...


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## Bluebutton (Apr 24, 2021)

T Bredehoft said:


> You appear to be  reading on the dovetails. I'd prefer to read on a piece of stock, known square on the working surface of the machine, the table. That's where the work will be....unless I'm missing something...


The photos are for reference.  I did use a 2/4/6 block clamped to the table.  I first found the issue when trying to make a 3"x 3" x 0.50" thick block.  I was machined 2 sides parallel but when squaring up the other surface it as 0.010" out.  I checked the side with a granite square on a surface plate and machinist squares as a secondary check.  No matter what I do I cannot get a square part between the x and y axes.


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## T Bredehoft (Apr 24, 2021)

Strange...Write PM about it, they may have an Idea or two. They are easy to work with.


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## Bluebutton (Apr 24, 2021)

T Bredehoft said:


> Strange...Write PM about it, they may have an Idea or two. They are easy to work with.


I have contacted them and been working with Matt.  They are great to work with.


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## BladesIIB (Apr 24, 2021)

Reading this it sounds like you were off .010” on a part that was only .500” thick. Then off .010” on a 4” side of your block. That seems odd. If you were off .010” in ½” would expect more like .080” in 4”. I know you said you locked the gibs but are they fully adjusted and tight?  If your X axis gib is not adjusted it would be easy to get the table to rock .010”?  I am sure I am missing something here, just trying to help.


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## Bluebutton (Apr 24, 2021)

Here is link to an video I uploaded to show the issue better.


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## Bluebutton (Apr 24, 2021)

BladesIIB said:


> Reading this it sounds like you were off .010” on a part that was only .500” thick. Then off .010” on a 4” side of your block. That seems odd. If you were off .010” in ½” would expect more like .080” in 4”. I know you said you locked the gibs but are they fully adjusted and tight?  If your X axis gib is not adjusted it would be easy to get the table to rock .010”?  I am sure I am missing something here, just trying to help.


Sorry for the confusion.  The part was out 0.010" between 2 sides of a 3 inch block.  The 0.50" thickness was just the stock i was using.


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## BladesIIB (Apr 24, 2021)

Just watched your video. When you have your dial on the Y Axis see if you can grab the table and move it by hand. Grab each end by the hand wheels and try to turn it like a steering wheel laying flat. If you are getting movement there then you need to tighten the gib to get all the play out. That seems like a lot of out of square to have ever passed any level of quality control.


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## BladesIIB (Apr 24, 2021)

Also, maybe captain obvious here but tightening the gib is not tightening the lock screws on the side until it is snug. Tightening the gib is adjusting it from the end and wedging it against the dovetail. You mention the tapered dovetail earlier so sounds like you have it. But also mention you have not run it in 3 years so just figured it was worth a mention.


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## Bluebutton (Apr 24, 2021)

BladesIIB said:


> Also, maybe captain obvious here but tightening the gib is not tightening the lock screws on the side until it is snug. Tightening the gib is adjusting it from the end and wedging it against the dovetail. You mention the tapered dovetail earlier so sounds like you have it. But also mention you have not run it in 3 years so just figured it was worth a mention.


The table only moves about 0.002" up and down and side to side without the axes side locks.  With the axes locked the the deflection is better about 0.001" each time it returning to zero.  I have done the same test as in the video with other 123 and 246 blocks with the same result and locking the axes.

  As for not using the mill in 3 years.  I've been using the Bridgeport at work for most of the parts I need.  I only bought the PM25 for when the machine at work is not available.  I also knew the PM25 would not compare to the Bridgeport and there would be some tolerance differences for an import mill.


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## rwm (Apr 24, 2021)

I think that video is telling. Your saddle is not ground square with the x axis. If the gibs are OK this is a manufacturing defect. Let us know what PM will do for you.
Robert

I just checked my PM 728 using the same technique as in your video. With my X axis aligned to the short side of the block, my Y axis is off about 1/2 thou over the 3" side of the block.
Robert


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## tkalxx (Apr 24, 2021)

I have found the exact same issue with my PM25. The mill is just under a year old and noticed that all my parts coming off the mill are no where near square. I spent the first 6-8 months converting my mill to CNC and so my out of squareness issue has just reared its head.

I measured .008" out of square over 3 inches on a 123 block. I checked my 123 block using a square comparator; it's out of square .0002". I've been through the whole gib adjustment phase multiple times and have never found a difference. Like you, if I grab the ends of the table and try to twist with an indicator on the side of my vise or a 123 block I can only see .002" of deflection in either direction. 

I've been in contact with Matt over the last week or so, he has been very accommodating so far.


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## BladesIIB (Apr 24, 2021)

Sounds like you both have exhausted all the tests and it is defect in the manufacturing. Glad Matt from PM is working with both of you. I am sure they will come up with a solution.


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## davidpbest (Apr 29, 2021)

Any update on this?  What has PM recommended be one here?


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## tkalxx (Apr 29, 2021)

davidpbest said:


> Any update on this?  What has PM recommended be one here?



Matt suggested I pull the saddle off my mill to take some pictures of the dovetail surfaces before jumping to conclusions. He wants to verify that there are no burrs/knicks/blatant surface imperfections that may be causing the issue. Due to my mill being CNC, I haven't had the time this week to fully commit to disassembling everything - hopefully this weekend I will.

I hope to take some measurements of the X-Y dovetail squareness on the surface plate while the saddle is off the mill. I don't have the necessary tools to get a truly accurate reading on how out of square the dovetails are (I am by no means a professional at restoring machines/scraping), but I should easily be able to get an understanding if the dovetails were machined incorrectly - which is what I have hypothesized. I will definitely report back once I learn more.


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## T Bredehoft (Apr 29, 2021)

Amazing.  I've had my PM25 at least 5 years, maybe 6, never thought to check. I put my Starret solid square in the vise, jiggered the vise around until X read 0 in four inches, moved the indicator to the blade and cranked the Y four inches. it's out perhaps .0002. Could be my Square's out, I've had it 30 years and it was used when I got it, never had it certified. BUT, what are the odds that my square is out within .0002 of the table.... The table clamps were snug enough that I couldn't see any wobble as I cranked the handles.


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## Richard King 2 (Apr 29, 2021)

If all else fails, I have a friend who lives in Berkeley CA who is a decent machine repairman who could come and repair it.   If PM want to hire him, have them email me and I'll forward it to him.   Richard@Handscrping.com


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## Bluebutton (May 4, 2021)

tkalxx said:


> I have found the exact same issue with my PM25. The mill is just under a year old and noticed that all my parts coming off the mill are no where near square. I spent the first 6-8 months converting my mill to CNC and so my out of squareness issue has just reared its head.
> 
> I measured .008" out of square over 3 inches on a 123 block. I checked my 123 block using a square comparator; it's out of square .0002". I've been through the whole gib adjustment phase multiple times and have never found a difference. Like you, if I grab the ends of the table and try to twist with an indicator on the side of my vise or a 123 block I can only see .002" of deflection in either direction.
> 
> ...


I was able to get my PM25 down to .003" over 4 inches today.  Here is what I found.  First the X axis gib had a radius on the face where the adjuster screw was making contact (gib photo).  The radius was forcing the gib up into the table surface.  I milled that face flat at work and the run out improved by .004" now only .006" out over 4 inches.  Once that was corrected I noticed the saddle was sitting flat on the lower dovetail surface.  The saddle had one corner higher by 0.002" (saddle photo).  While I had every thing apart again I checked the base for level and found out it had a 0.02' twist to it.  I loosened the bolts holing it to the stand and most of it went away.  With everything back together I now have the mill within 0.003" over 4 inches in Y with the X indicated at 0.0005" over 6 inches.  Matt at PM has been very helpful.  He has offered to correct any issues with the mill, vary have with PM support.


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## Bluebutton (May 4, 2021)

Richard King 2 said:


> If all else fails, I have a friend who lives in Berkeley CA who is a decent machine repairman who could come and repair it.   If PM want to hire him, have them email me and I'll forward it to him.   Richard@Handscrping.com


Thanks for the offer.  I only live 2.5 hours from Berkley.


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## Bluebutton (May 4, 2021)

davidpbest said:


> Any update on this?  What has PM recommended be one here?


PM has offered to repair the saddle on my machine and replace it if necessary.  My saddle measured .004" out of square on the CMM at work and 0.0037" when checking it out on another mill at work.  Even with the saddle out I believe the squareness was corrected with the tapered gibs.  I found a few issues with a radius on a gig interfering with the adjustment screw face.  The biggest issue seem to be that the base had a twist to it from the stand.  I loosened the stand and it is a lot better, but not perfect.  I will make a test part tomorrow to check the final squareness.  Once again PM has been very supportive in trying to find the issue.


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## Richard King 2 (May 4, 2021)

Down to .003" in 4" ?  That's pretty bad in my opinion.  Years ago when I was still rebuilding machines I was a contractor for Jet and MSC and they would pay me to go out and repair problem machines.  Has PM offered to fix it at their cost?   The gib picture is hard to believe with that bevel bottom.   I suspect the Y is still twisted.   A easy test would be to set a precision level on the table and zero ut side to side and crank it in and out and watch it.  You can buy imported levels on eBay for 100.00 .   .0005/12"  You could get a 12" or 6" level.  You might be able to shom under the base and above the frame to twist it good.  Rich
PS:  keep track of your labor and charge them for it.  $50.00 p/h would be a bargain for them.
Another thing, put a parallel under the 1 2 3 block to rise it above the jaws, then indicate both sides at the same set up.


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## Bluebutton (May 4, 2021)

Richard King 2 said:


> Down to .003" in 4" ?  That's pretty bad in my opinion.  Years ago when I was still rebuilding machines I was a contractor for Jet and MSC and they would pay me to go out and repair problem machines.  Has PM offered to fix it at their cost?   The gib picture is hard to believe with that bevel bottom.   I suspect the Y is still twisted.   A easy test would be to set a precision level on the table and zero ut side to side and crank it in and out and watch it.  You can buy imported levels on eBay for 100.00 .   .0005/12"  You could get a 12" or 6" level.  You might be able to shom under the base and above the frame to twist it good.  Rich
> PS:  keep track of your labor and charge them for it.  $50.00 p/h would be a bargain for them.
> Another thing, put a parallel under the 1 2 3 block to rise it above the jaws, then indicate both sides at the same set up.


It was 0.010" across 3 inches.  I not saying .003" over 4" is perfect, but it better than before.  PM has offer to fix the issue once the issue has been determined.  Not sure if they cover shipping costs, it has not been discussed yet.  I have a Starrett 6 and 12 machinist level and will check the table tomorrow.  I did have parallels under the 123 block in the video.  I have removed the vice and replaced it with a 246 block clamped directly to the table to eliminate any vice tolerances.


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## Bluebutton (May 5, 2021)

Latest update.  I have the saddle back out of the machine and will have it surface ground to remove the 0.002" high spot.  I found if I put a 0.002" feeler gauge between the saddle and the base and the base is not bolted to the stand I can get 0.001" run-out over 4" in the Y axis and few tenths over 6" in the X axis.  Without the feeler gauge the best I can get is 0.0025" across the Y axis.  Another reason for the grinding, I am seeing the X table move slightly when the table weight shifts from right to left when passing the mid point in the table travel.

 I have been in contact with PM and there support has been great.  I should everything back together this weekend.


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## Richard King 2 (May 5, 2021)

Not knowing exactly how it looks under there, but you might be able to drill and tap a hole say 3/8"- 24 near the hold down bolt and and use the 3/8 -24 cap Allen cap screw with a jam nut /lock to tweak it closer then a .001" .


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## tkalxx (May 6, 2021)

As @Bluebutton and Matt at PM suggested, I completely loosened off the mounting bolts of the mill. While the mill was still secured to my stand, I took a feeler gauge under the saddle of the Y-axis and could fit a .009" shim under the back of the saddle. With all the mounting bolts loose I can fit a .002" shim under the rear of the saddle but only under the rearmost 3/4" of the saddle. 

With all the mounting bolts loose and my vise trammed within .0003" in the x axis I'm seeing the y axis out by .003" over 3 inches now. It's not amazing, but it's better... The crazy thing is that the mounting bolts weren't even that tight.


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## Bluebutton (May 6, 2021)

tkalxx said:


> As @Bluebutton and Matt at PM suggested, I completely loosened off the mounting bolts of the mill. While the mill was still secured to my stand, I took a feeler gauge under the saddle of the Y-axis and could fit a .009" shim under the back of the saddle. With all the mounting bolts loose I can fit a .002" shim under the rear of the saddle but only under the rearmost 3/4" of the saddle.
> 
> With all the mounting bolts loose and my vise trammed within .0003" in the x axis I'm seeing the y axis out by .003" over 3 inches now. It's not amazing, but it's better... The crazy thing is that the mounting bolts weren't even that tight.


After I loosened my base I readjusted the gibs and it got better.  Now I have the saddle off to a local shop to have it ground.  It has a 0.002" twist to it.  I should have it back Monday.  Will keep you posted.


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## Bluebutton (May 6, 2021)

Richard King 2 said:


> Not knowing exactly how it looks under there, but you might be able to drill and tap a hole say 3/8"- 24 near the hold down bolt and and use the 3/8 -24 cap Allen cap screw with a jam nut /lock to tweak it closer then a .001" .


That the plan.  We do the same for the automation equipment we build.  The old push pull method for leveling and securing.


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## tkalxx (May 7, 2021)

I spent the last 3-4 hours playing around with the mounting bolts, tightening/loosening them individually, and re-checking squareness in between. I made a mental image of how the base of my mill was twisted and ended up shimming between the base and my stand to reverse the twist. I added a .038" shim to the rear right corner and am now seeing less than .0005" out of square in Y. I'm at the point where I can't do any better without purchasing some higher precision tools due to the error stack up (vise trammed within .0003" and my 123 block being out of square approx. .0002"). Either way, I think I'm going to call it good for now - it's a major improvement over the .008" I was seeing originally. I machined a 2"x3" block and checked it with a square comparator on my surface plate. It showed approx. 4-5 tenths out of square over 3 inches.

I just want to iterate how accomodating Matt and the customer service at Precision Matthews has been. When I originally emailed Matt I explained that I knew the mill was well out of warranty due to the CNC conversion and if it came down to it, I was OK purchasing a new saddle from him. He assured me that if the saddle was truly machined out of square, he would replace it under warranty because he recognized that the conversion had nothing to do with it. Overall, Precision Matthews has been a great company to deal with.



Bluebutton said:


> Now I have the saddle off to a local shop to have it ground.  It has a 0.002" twist to it.  I should have it back Monday.  Will keep you posted.



Let us know how the grinding turns out.


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## jwmelvin (May 7, 2021)

Feeler gages showing saddle twist when the base bolts were right made me wonder about shims so I’m glad to see it appears to work at least in some instances. Nice work.


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## Richard King 2 (May 7, 2021)

The base is sheet metal and not precision.  It has to be shimmed.  I bet if you set it down on a surface plate it would be fine.  If PM was smart they would have 3 legs ( 3 main points) and on the corner have smaller jacks and hold downs on the 4 corners.  Yo eliminate twists.


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## Bluebutton (May 9, 2021)

tkalxx said:


> I spent the last 3-4 hours playing around with the mounting bolts, tightening/loosening them individually, and re-checking squareness in between. I made a mental image of how the base of my mill was twisted and ended up shimming between the base and my stand to reverse the twist. I added a .038" shim to the rear right corner and am now seeing less than .0005" out of square in Y. I'm at the point where I can't do any better without purchasing some higher precision tools due to the error stack up (vise trammed within .0003" and my 123 block being out of square approx. .0002"). Either way, I think I'm going to call it good for now - it's a major improvement over the .008" I was seeing originally. I machined a 2"x3" block and checked it with a square comparator on my surface plate. It showed approx. 4-5 tenths out of square over 3 inches.
> 
> I just want to iterate how accomodating Matt and the customer service at Precision Matthews has been. When I originally emailed Matt I explained that I knew the mill was well out of warranty due to the CNC conversion and if it came down to it, I was OK purchasing a new saddle from him. He assured me that if the saddle was truly machined out of square, he would replace it under warranty because he recognized that the conversion had nothing to do with it. Overall, Precision Matthews has been a great company to deal with.
> 
> ...


Grinding was done today and the mill is back together.  The saddle is now less than 0.0002" flat.  Unfortunately the issue remains with the saddle twisting/flexing when the table is not centered to the Y axis.  When the table is centered the mill indicates in perfectly, but when moving 3 inches either direction from center I find the saddle twists and I get a gap like before.  Move the table to the left and get a 0.003" gap in the front right corner.  Move to the right and get a gap in the left rear corner.  Like tkalxx did, I too spent 3-4 hour trying to level the base with shims.  I am now temped to take the mill apart down to the base casting and have it ground as well.  Not sure what to do after that.


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## Richard King 2 (May 9, 2021)

I still think part of the issue is the stand.  Your bolting it down to a not precision stand.  Or the saddle top to bottom is not co-planer,  If the indicator changes when you reverse the travel that probably means the center of the positive side of the saddle Y is high in the middle.   I wish I lived closer I am sure I could figure it out and fix it for you.  I do have some students who live near Sacramento who get together now and then.  I bet if your took it to one of there weekend get- togethers and they could figure it out.   They all can scrape too.   Did you take some photo's when you had it ground?  You may want to ask or cut and paste this into the Rebuilding forum and most of my friends in CA are members of Hobby Machinist and read the rebuilding forum.    I'll ask them to come here and help.    Rich

Link to the rebuilding forum:









						MY CA Students, can you help this Sarona CA fellow please
					

Hi everyone.  Over the years I have taught several California classes and many of my students read and help in this forum.   There is a fellow who has a mill that has issues.  He is trying to fix it in another forum.  I was hoping he could bring it to one of your club monthly get togethers and...




					www.hobby-machinist.com


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## Rex Walters (May 9, 2021)

Happy to help if I can, and I'm sure the rest of the folks from our group would be as well. We are hardly (read, "*NOT"*) expert rebuilders but Rich has taught many of us a few things, so there is always hope (laugh).

Of *course *you're in Sonora! I'm down in the San Jose area, and most of the other folks are up toward Sacramento. Almost a perfect triangle: you're about 100 miles from either. PM me ("start a conversation" on this forum) if you'd like to figure out a way to get together.


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## benmychree (May 9, 2021)

The group has not had a monthly meeting since the pandemic came upon us, and so far none have been planned.


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## Bluebutton (May 9, 2021)

Richard King 2 said:


> I still think part of the issue is the stand.  Your bolting it down to a not precision stand.  Or the saddle top to bottom is not co-planer,  If the indicator changes when you reverse the travel that probably means the center of the positive side of the saddle Y is high in the middle.   I wish I lived closer I am sure I could figure it out and fix it for you.  I do have some students who live near Sacramento who get together now and then.  I bet if your took it to one of there weekend get- togethers and they could figure it out.   They all can scrape too.   Did you take some photo's when you had it ground?  You may want to ask or cut and paste this into the Rebuilding forum and most of my friends in CA are members of Hobby Machinist and read the rebuilding forum.    I'll ask them to come here and help.    Rich
> 
> Link to the rebuilding forum:
> 
> ...


You are correct.  I disassembled the entire mill today for one last check of everything.  I found the stand is not helping and either was this glob of paint from the factory.  I scraped everything clean and hit it with a stone for sharp edges.  It still rocks a little, but before I put it back together I will be adding a 12"x18" by 1"thick plate to the mount the mill base to and will shim the under side of that plate to the stand.  While I had it apart I did add 1/2-20 threads to the corners of the mill casting base for leveling if needed.  Thanks for the offer to have the club look at it.  I think I have it under control at this time.


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## Bluebutton (May 9, 2021)

Rex Walters said:


> Happy to help if I can, and I'm sure the rest of the folks from our group would be as well. We are hardly (read, "*NOT"*) expert rebuilders but Rich has taught many of us a few things, so there is always hope (laugh).
> 
> Of *course *you're in Sonora! I'm down in the San Jose area, and most of the other folks are up toward Sacramento. Almost a perfect triangle: you're about 100 miles from either. PM me ("start a conversation" on this forum) if you'd like to figure out a way to get together.


Every day that I work on this I find one more little item that adds to the twisting issue.  Today it was a build up of old paint under the base.  Now that I have everything clean and not constrained I have a better understanding of what is causing the twist.  Thanks for the offer to help, if I can't get it right afet this next go around I will let you know.


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## Richard King 2 (May 10, 2021)

I see you have a surface plate.  Flip the base over on it and see if it sits on it flat.  Take a soft blow hammer and tap around the perimeter and listen for a solid thud where it touches.  Then listen for a clapping and hollow  sound and when you find it slide on feeler gages.  It may take overnight or a few days for it to twist straight if it was ever right.   Once you get it solid all around the perimeter take a height gage and a dial indicator to see if the top of the base ways are all on the same plane or co-planer.   Then set the saddle on the base and indicate the top of the saddle and see if it is co-planer to the base ways.  It's like building a house.  You have to have a solid foundation and built square and co-planer all the way up.  If not you get the multiplication of errors and it will never be correct.   Grinding a crooked part on a grinder is not the answer, unless you shim the twisted part before you turn on the  magnet.  If not you mag it down and it is cockeyed, then release the magnet it goes back cockeyed.    I always scrape the cockeyed base first so it sets on the magnet or surface plate first.


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## Bluebutton (May 13, 2021)

Mill update.  The mill base is now level and is as flat as possible.  I Put a .75' thick aluminum plate between the mill base casting and the chip tray/stand.  I first set the mill base casting upside down with the dovetail face on my surface plate and set the aluminum plate on top of casting, basically letting the aluminum sit in a free state on the casting.  I then checked for gaps between the aluminum pate and the casting. I was relieved that there were no gaps more that .001".  I put the chip tray on the stand with the aluminum plate.  With the plate loose I leveled the stand this allowed me to pick the appropriate shim needed to fill the gaps between the stand and chip tray.  With the shims in I started to tighten the bolts that hold the casting down, anytime the level moved I added or removed shims.  If you noticed I didn't have short enough bolts so I used nuts as spacers.  As I put the mill back together I kept checking it for level as I went.  As seen by the pics it stayed fairly level in X and Y during assembly.

The squareness has improved and the gaps between the saddle and dovetails are gone.  There is little if any flex when the X table travel end to end, but I still have a slight squareness issue.  Seems the mill still is out .003" over 4" in the X or Y axis.  I doesn't matter which axis you indicate in the other axis is always 0.003" out.  I still believe the issue is in the saddle.  The CMM report did show it out of square 0.004"

Shims used.
0.065" Right Rear
0.005" Left Rear
0.020" Right Front
0.040" Left Front


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## Richard King 2 (May 15, 2021)

That level graduations are .005"  per line?  You may want to eyeball the bubble on the exact line to get it closer.   If that is acceptable for you, then use it.  If not arrange for one of the club members to come help.  Many of them are retired.  John York has all the tools needed as does Rex. They could scrape it square.   The set up you have looks nice.


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