Why are my cuts bigger on the bottom side?

[Peeps]

I'm sorry if this is in the wrong area, but where do you post general questions around here?
If anyone can help while i'm in here......when i cut 3/4 or 1/2 mdf, my cuts are bigger a little bit on the bottom all the way around. my table is level, router is straight and i looked at the bit and it's straight. how can they be bigger on the bottom?

[WoodSpinner]

Originally Posted by Peeps I'm sorry if this is in the wrong area, but where do you post general questions around here? If anyone can help while i'm in here......when i cut 3/4 or 1/2 mdf, my cuts are bigger a little bit on the bottom all the way around. my table is level, router is straight and i looked at the bit and it's straight. how can they be bigger on the bottom?

could be runout, like the tool isnt perpendicular to the motor shaft?

[Peeps]

Originally Posted by WoodSpinner could be runout, like the tool isnt perpendicular to the motor shaft?

I was thinking the bit was warped, it looks OK though. thanks for you input too.

[txcncman]

Tool push off. Tool deflection. Machine deflection.

[Peeps]

Originally Posted by txcncman Tool push off. Tool deflection. Machine deflection.

First thing I'm going to do is get another bit. if that's not it, could you explain how machine deflection can happen? thanks.

[Khalid]

i think tilted z-axes..it must give you also the top wrong dimensions but you will feel less error at top compared to bottom...

[Peeps]

Originally Posted by Khalid i think tilted z-axes..it must give you also the top wrong dimensions but you will feel less error at top compared to bottom...

Here's what's strange, if I cut a 3 x 8 inch of mdf and look at it from all sides, it's bigger on the bottom all the way around. I was thinkin the z axis too, but if the z was out of plumb, wouldn't it angle out the same direction along the x axis? I'm going to try another bit today, but after that I'm stumped on this matter for now. thank you.

[WoodSpinner]

Originally Posted by Peeps Here's what's strange, if I cut a 3 x 8 inch of mdf and look at it from all sides, it's bigger on the bottom all the way around. I was thinkin the z axis too, but if the z was out of plumb, wouldn't it angle out the same direction along the x axis? I'm going to try another bit today, but after that I'm stumped on this matter for now. thank you.

what are you using for a spindle?

[Peeps]

Originally Posted by WoodSpinner what are you using for a spindle?

I'm using a router, it's the bosch colt 1 hp. The bit I'm using is a cheaper one, not sure if its the problem or not though.

[WoodSpinner]

Originally Posted by Peeps I'm using a router, it's the bosch colt 1 hp. The bit I'm using is a cheaper one, not sure if its the problem or not though.

not sure about the colt, but a lot of people use them so its prolly not that, a rotozip or a dremel would flay out during a climb cut, if your router isnt held ridgidly then maybe it would do the same.

[louieatienza]

Is your bit sharp? Believe it or not, the deeper your cut depth, the more ridgid the bit is, because the top of your material is closer to the collet. I wouldn't say runout, because the runout would be the same no matter what depth your Z was at. It might be more a backlash or ridgidity issue; Try cutting an outside profile, using climb cutting, and then do a finish pash, using conventional cutting, and see if that "cleans" up the "bevel" on the piece... If this helps, then you may have to work on getting your axws more ridgid, or remove more backlash from your drive system...

[adprinter]

When I first completed my machine build, I consulted a machinist friend at work on how to go about setting the actual router bit to be at 90 degrees in relation to the table. His recommendation was a "duh" moment for me. What I did, was drill a hole into a piece of angle stock on the drill press (to make certain it was drilled at a precise 90 degree angle). Through this hole, I pressed a 1/2" shoulder bolt, and mounted a nut onto the threaded end to lock it flat to the surface of the angle stock. I then mounted the end of the 1/2" shoulder bolt into the chuck of the router. Onto the opposite end of the angle stock, I mounted a dial indicator. And spun the chuck of the router around by hand, to measure the differences across the surface of my table. Since I had built this machine myself, I designed almost every aspect to be adjustable. Then, it was a simple matter of loosening bolts, and turning the adjustment bolts to "dial it in" to within an average of 0.004" across the entire surface of the table. I used a similar method in checking the Z axis travel, by mounting a piece of angle stock onto the table surface, and the dial indicator onto the router clamp assembly. Then manually jogging the Z axis up and down to check for travel angle in the X orientation, then turned the angle stock and dial indicator 90 degrees to check for travel angle in the Y orientation. This step was probably the most time-consuming adjustments I had to make in setting up my machine. But it has resulted in a very precise machine in the end. When I was in the designing phase of my build, I considered many aspects of machining. When any metal is welded, it expands due to heat, and is near impossible to get perfection in terms of perfect perpendicular angles. This is why I designed all aspects of the machine to be adjustable. And once I got everything dialed in to near perfection, drilled holes into the various assemblies, and installed taper pins (alignment pins) to keep everything locked into place. Now, when anything starts cutting incorrectly, it is usually due to worn bearings along one or more axis. (Which I then replace). When it comes to metal working, there is simply no such thing as perfection. This is where it really pays off in the end to design things to be adjustable. Hope this helps you to diagnose your problem, as it sounds like your Z is not quite "perfect".