Gantry flex

[MDHunt]

I used the Drill toolpath to drill multiple 1/8" holes using a 1/8" end mill bit. The first few holes were straight, and then began to elongate in the Y axis until the holes began to look like ovals. They drilled at an angle as well as deformed. The only reason I can think of for this is the gantry was flexing in the Z axis, throwing the drill holes off.
Has anyone else experienced this? Any tips on how to fix it?
Thanks

[PaulRowntree]

Gantry would have to be very weak to flex that much on a drill pat ... does it flex when you press on it?

Could the material have lifted off the table during a drill cycle?

[steve323]

The Shark HD4 listed in the OP's profile appears to be reasonably solid. I have a homebuilt system with a similar layout. My Y axis has 2 36" long parallel rails spaced about 4" apart. Each rail is 1" diameter steel. The problem is that any flex in the rails is magnified because they are so close to each other. For example, one rail can flex inward by 10 mils and the other flexes outward by 10 mils. The cutting tip 8" away can have 50 mils of deflection. The problem is worse when the head is near the center of travel where the rails are most likely to flex. I ended up adding an additional parallel rail about 12" away to reduce the flexing.

Question to the original poster: Does the head move with gentle pushing? Is it worse when the head is near the center of travel vs near either end? Also, how sharp is your bit? Can the problem be reduced by lowering the Z speeds?

Steve

[MDHunt]

Paul, yes, there is a small amount of flex in the Z axis when I press on it with minimal pressure. I don't want to damage my machine, so I don't do it with much force. When I am drilling or carving, what should be a straight drilled hole, is elongated along the Y axis by a small amount and the drilling depth is less than it should be.
Steve, when talking about the Z speed, are you referring to the plunge rate?

[4DThinker]

Does your Shark have an aluminum backplate on the gantry? If not, then I highly recommend you contact NextWave and order one. Our HD2 didn't come with one and warped badly under the cantilevered weight of the router.

4D

[Steve Misher]

The HD4's router mount is all plastic and flex is a big problem! Almost all of the machine is plastic which is why there is flexing. You have to slow the Z travel way down so it won't flex as much while drilling or using any type of cutter, unless you are taking very shallow cuts. As for drilling, just slow down your plunge rate and it will work out fine.

[MDHunt]

I also emailed next wave and got this for a reply.

1.) If you have the gantry set at the highest position, try lowering the gantry by using a different set of mount holes. The shorter the gantry height the less flex.
2.) Look at how far your router is extending through the router hanger bracket. Like the gantry the longer it is the more flex there is. Raise the router up.
3.) Slow the Inches per minute of travel down especially on larger bits.
4.) Change the depth per pass to add more passes to your project.
5.) Run you router at a higher speed.

1 and 2 will result in the gantry having less flex. 3-5 will result in taking less force to do the work, resulting in less flex.


I'll give these suggestions a shot tomorrow and post the results.
Thanks for the help!

Paul, yes, there is a small amount of flex in the Z axis when I press on it with minimal pressure. I don't want to damage my machine, so I don't do it with much force. When I am drilling or carving, what should be a straight drilled hole, is elongated along the Y axis by a small amount and the drilling depth is less than it should be.
Steve, when talking about the Z speed, are you referring to the plunge rate?

Gantry would have to be very weak to flex that much on a drill pat ... does it flex when you press on it?

Could the material have lifted off the table during a drill cycle?

[Daniel S]

I have the Shark HD4 also and have had flex issues. To much plastic so you have slow down speeds & feeds. I am using the spindle and have found that it preforms best at speeds around 12K rpm and 40 in/min with plunge rate 20 in/min for most operations with end mills. I also found that 3/16 end mill from Precie Bits works the best when cutting out a project and I only cut .0625 depth per cut and I always ramp down 2 ins per cut. When carving I up the speed to 16K and that works good with all size ball nose bits. I also moved my gantry down but I can't say that made any difference to me. 3D carving I set the bit speeds to 50 in/min but 3D has alot of Z movement so speed is not an issue. If you slow down you will most likely get the best results. Keep trying different speed until you get the results you like.
Dan

[Steve Misher]

Yes, you have to slow down the plunge rate. If you are just drilling 1/4" holes, I would use a brad point bit. It will not wander like a standard bit.
When I had my HD4, it really didn't matter which mounting holes I used to mount the gantry. It still flexed quite a bit.

[wmgeorge]

Yes, you have to slow down the plunge rate. If you are just drilling 1/4" holes, I would use a brad point bit. It will not wander like a standard bit.
When I had my HD4, it really didn't matter which mounting holes I used to mount the gantry. It still flexed quite a bit.

That's why I purchased my Chinese 6040 router and from a USA vender in Chicago. I am very impressed as I have used CNC routers in the past, the "other" one was made in Michigan and was a constant source of problems when I first got.

I looked at the Shark and was set to purchase one, in fact I almost purchased a router motor that was on sale. Then I started looking at the construction. This one is very solid and worked out of the box, even on a old laptop on a parallel port.

[ger21]

Don't blame Michigan.

[IslaWW]

Don't blame Michigan.

Plus one to that!

[KENYPETE]

My first CNC was a Shark Black Diamond with the plastic back gantry plate. I was able to measure the deflection when the router was centered in the X direction. I ordered the aluminum back plate from NWA and that fixed the problem. If you search the Shark forum there are several posts on this issue.

[FixitMike]

I've looked at the HD4 and observed that when one pushes up on the router chuck, the bit will move in the Y axis direction. This deflection will result in the elongation described when the Z drive is pushing the bit into the work. As far as I can tell, most of the deflection is in the router carriage. Perhaps replacing one of the plates with aluminum would help. I know that adding a couple of screws to my ProPlus Shark helped quite a bit, but the screws in the HD4 are better located to reduce deflection. http://www.cncsharktalk.com/viewtopic.php?f=9&t=5020

Mike (Retired Professional Engineer)

[wmgeorge]

Don't blame Michigan.

LOL I married a Michiganite. The router came from a company called IMService and all I had was trouble for the first six months, I got blamed for everything, it was NOT the machine! I am a licensed Ham I know about RFI and EMI which he tried to blame it on, I am also a Master Electrician so I know about proper wiring which was the other scapegoat. Turned out to be a control software issue.