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Just Bob Again
08-04-2008, 05:19 PM
I have a Grizzly mill/drill. One of the heavier ones. Works probably as well as can be expected. With 20 or 30 pounds force, I can move the spindle about .003 total. Everything that can be tightened seems tight. The bearings are reasonably tight. I get the same deflection at the quill end or on something mounted in the spindle. Ways are fairly tight. Got it adjusted for about .005 backlash in the screws.

This is enough slop to make most things look like they were chewed by small rodents. Has anybody managed to make any useful improvements to these things, like filling the column with lead or cement or such? It's never going to be a great machine, but maybe it can be a bit better.

lazlo
08-04-2008, 05:26 PM
5 thou is a lot better backlash than I had on my Mill/Drill, and I was able to get pretty decent surface finish.

Are you calculating the correct speeds and feeds for the material?

Are you locking the cross-gib while feeding (or vice-versa)?

Locking the quill while feeding?

Chipslinger
08-04-2008, 05:55 PM
Take lighter cuts.

dockrat
08-04-2008, 06:36 PM
use a rougher for all but light finishing cuts

Just Bob Again
08-04-2008, 06:39 PM
Take lighter cuts.

Even with slow finishing cuts (.005) and a new endmill it's a bit rough. Everything is locked. Quill and other axis. It isn't too bad on surfaces with a fly cutter. Milling edges with the side of a 2-flute or 4-flute is a couple thousandths rough.

Willy
08-04-2008, 06:44 PM
Bob, here is a link to the thread that Torker posted earlier this year.

You mill drill guys.... (http://bbs.homeshopmachinist.net/showthread.php?t=28222)

It deals with stiffening the column with a 3" steel shaft encased in concrete and allowances for tramming adjustments.
I know he works the bajeezus out of that thing and he's very happy with the performance improvements.

MickeyD
08-04-2008, 09:20 PM
I had one of those evil little machines way back, chinese spindle bearings, a sloppy quill, and inconsistant table tightness, but with a little attention to detail it would give a nice finish. The big thing that it was very sensitive to was tool sharpness, and it liked HSS a lot better than carbide. One thing that I did was to add a power feed on the X axis and that really helped the finish. Even today, a power feed gives a much nicer finish than me cranking on the wheels.

I would try going back to the basics - proper workholding, the right tool for the material, and speeds and feeds before you throw your hands up. There is a lot of really beautiful work done on crap machines, just takes a little more skill and patience.

Just Bob Again
08-04-2008, 09:32 PM
Thanks. Cool. That's the kind of idea I was looking for. Looks like the base/column connection is the weak point in my setup. I doubt the column itself is flexing much but damping might help. I'll bet I can get some useful improvement by just replacing the column bolts. Maybe put a put a piece of inch and a half threaded rod in the column and put the whole base/column unit into compression. Easy to try before I mess things up and fill it with epoxy and such.

lazlo
08-04-2008, 09:34 PM
Bob, if you can post the material, the cutter you're using, and the speed and feed you're running, it would give us a lot more insight into your problem.

Bill Pace
08-04-2008, 09:37 PM
This guy has done a LOT of tinkering/messing/finetuning his M/D and recorded and documented it really well .... check it out.

http://rick.sparber.org/ma.htm

MickeyD
08-04-2008, 10:31 PM
Rick Sparber's site is great. I have been following his shaper project for a couple of months and it is very enjoyable.

gnm109
08-04-2008, 11:57 PM
I have a Harbor Freight Mill Drill. It's their model 33686 that they've been seliing for years now. I bought mine around 1995. I agree, they could use more stability. I have read about filling the main tube with concrete but I can't somehow bring myself to do that.

One change that I did make, shortly after I got the machine had to do with the poor method that they used to index the R8 end-mill holders. I discovered that there was some looseness when the holders were inserted before tightening the draw bar. The holder would rotate a few degrees wither way.

After some thought, I completely disassembled the quill shaft unit and took a close look at it. I found that the manufacturers had simply drilled a hole in the quill and threaded it for a small metric socket head set screw. The end of the set screw would enter the notch in the R8 to hold it from turning. When I removed the set screw, I saw that it had gotten chewed away after about two weeks of use.

The repair was fairly simple. I looked in my motorcycle scrap box and found a loose roller bearing that was the same size as the indexing notch in the R8. I drilled the hole in the quill shaft to a few thousandths smaller then the roller and then, with an R8 holder inserted into the quill so that I could see the notch, I pressed the roller tightly into the hole until it bottomed out on the R8 holder.

The fit was extremely tight and to this day, I've not had any trouble with the repair at all.

One other rissue that I found was that the cast cover that goes over the worm used to lower the quill had a poor fit and it would rub on the shaft holding the three handles.

I used a boring head to clear the hole nice and round so that it was concentric with enough clearance to relieve the rubbing. Since it's only a cover, I was able to use the machine itself to make the repair.

I have found that the machine works better with HSS tools and small cuts. Obviously these machines have their limitations. At the present time I'm considering a used Bridgeport when I can find one nearby. I would still keep the HF unit, though. Besides having some use as a milling device, it's a really good drill press.

I left mine on 120 VAC because it runs just fine. I think it can be converted to 220 but the on-off switch doesn't seem that it would work. I'd have to change that and there's really no reason since the machine has ample power on 120.

That's my story and I'm stickin' to it.

oldtiffie
08-05-2008, 07:53 AM
I'd appreciate it if the OP were to post pics (preferred) and/or links (alternative) so that I can see what type of mill-drill we are discussing.

derekm
08-05-2008, 08:56 AM
Filling a tension resisting tube with an adhesive, setting, compression resisting compound is bound to make an improvement but it doesnt have to be heavy or wet. How about polyurethane foam :) might sound crazy but this type of of approach is used in aircraft and F1 to make very strong stiff structures. Even the building trade in the UK uses polystryene and polyurethane structurally in compression. Most house floors made of concrete are laid on polystyrene. High performance ally masts on yachts are foam filled to add strength
Try gluing two really thin sheets of ally (30guage) , even balsa wood with a sheet of polystyrene in between. You will be surprised how strong it is.

oldtiffie
08-05-2008, 09:04 AM
This can happen with "climb milling" - if this is the case, try conventional/"up" milling.

airsmith282
08-05-2008, 09:10 PM
i just gota busy bee ct129 mill drill and i dont seem to have thoes isses at all in fact i love its great works very well .i took off all lthe saftys other then the power button one thats stil there. but the rest are gone now and its just the cats meow ,, i was looking into grizzly stuff and harbour frieght and now iam glade i stayed away from the stuff,and went with the choice that i did ..


you defentlly get what you pay for thats for sure , if i had been stung that bad id send it back and demand they replace it with a good one or geta refund and get something better..

my firts lathe cost me 800.00 bucks it was a princessauto metal worker 7x12,any how it fired only after 2 months i gota refund then spend the extra 200.00 and got the busy bee 10x18 and have had it going on 3 years now and i love it

1 problem i had wiht my ct129 is i gota bad drill chuuck wiht it. and it was replaced with a better one rightwawy , my lathe had 1 issue wiht the tail sotck sleeve and was replaced and then i made a bobo but manage to fix it and now have 1 spare sleeve just in case i get a bad arbor spinn again that messes it up ,, other then that all is good with it ..

i keep hearing stories about harbour frieght stuff and grizzly and a few other my question would be if the stuff is so bad hten why are people still buying the stuff machineing equipment even for home shops is not cheap and you gota be able to do good work on the stuff you buy, in my opnion with out having to fix it beforeyou use or or mod the hell out of it to get to even work right..if the QC in china is so bad then the consummer needs to complain to the right places and demand that there be good a proper QC on the stuff we buy..

derekm
08-06-2008, 05:12 AM
Correct me if i'm wrong but a lot of typical mill-drill applications in the H/S environment are small cutters in Alu -So ultimate stiffness is not a real issue in these applications. So why do they typically max out at 2000 rpm? Surely 10,000 rpm would be of more use. For example 400 sfm on a 10mm HSS cutter is about 3800 rpm... Am I missing something?

Derek

Metalmelter
08-06-2008, 07:03 AM
Bob,

I have one too and ended up buying a Bridgeport soon after. However, that mill came as a package deal with a lathe. So now the mill/drill just sits...

If I were you, I would really try to find out what is causing the problem. FWIW and for the money you paid, (I'm assuming this is a new mill you bought from Grizzly), Grizzly has rather good customer service and will work with you in getting replacement parts to help make the situation right. I've heard and read many good stories of happy customers after they had to spend some time finding the faulty part. Replacement parts are free ;)

I'm not sure what I'll do with the one I have now. It collects dust. It's a gear head model and one nice feature it has - when you shut it off it turns off instantly with NO coasting. That would be great for a tapping machine.

Post some pics of what you have and what maybe what you are trying to mill. Maybe the problem is not in the mill. Pictures always help ;)

A.K. Boomer
08-06-2008, 10:08 AM
With 20 or 30 pounds force, I can move the spindle about .003 total. .



This is not a reinforcement issue, if it is then your really in trouble as it means your entire base and mill column is made of hardened rubber --- anotherwords if 20 pounds of force is getting you that kind of deflection it means once you load an intermittent cutting endmill in there you might times that number by 3 depending on how much your taking off, you need to find out exactly where its coming from and also focus on "play" rather than "flex" as I dont think even the cheesyest of machines should show this kind of "flex" and if they do you need to sell it or just use it for cutting up styrofoam ---------
Sometimes spindle bearings can be adjusted perfect but they can have free-play where the spindle shaft goes through the id of the bearing (just an example)
Your description of the flycutter working good made me give this example, sometimes a flycutter will side load loose spindle bearings (or loose mounted spindle bearings) and actually keep them from chattering, Now here's a question for you -- how does that same flycutter work on an interupted cut? (wear eye protection)
I would not panic and cake your machine up with cement, Id systematically troubleshoot all area's in question for having excess free-play and then take it from there...

Just Bob Again
08-06-2008, 10:53 AM
..... I dont think even the cheesyest of machines should show this kind of "flex" .....

Hmmmm. This is definitely in the "cheezy" category, then. I've had others that worked even worse, though. Kinda what I expected out of the machine. It's been like this since I bought it new about 3 years ago. I don't think it's spindle bearings or quill problems. Spindle runs with a few tenths TIR. Quill moves a couple tenths when the lock is tightened. I've done some fine work with it, but it takes care since it's so flexible. Never had time to really hunt it down. The column can't be flexing that much. 4.5" OD cast iron with about 1/2 inch walls. Casting looks good on the inside. I think the bolts are a major factor here. (4) 16mm bolts hold the column to the base. They're marked "4.8". That's probably a tensile strength somewhere between cheddar cheese and talc. Even a good bolt that size will stretch a little. If I remove one of the 4 bolts, the total spindle deflection with approximately the same force goes from about .003 to about .005. I just ordered some grade 10.8 cap screws. A cheap test. If it doesn't help, it eliminates that from the possible causes. The base could be flexing, too, but my 3-bolt test probably indicates a problem with the bolts. Also should unbolt the whole column and see if the mating surfaces are flat. Could be a problem there. I'll do that when I change out the bolts.

I bought the machine because I had no space for a real mill and the floor wouldn't hold one anyway. Just moved the shop to a concrete floor and I'm looking for a Bridgeport-type mill now. Until I get one, would be nice to maybe improve this one a little. Can always use it for stuff if it works a little better.

Willy
08-06-2008, 12:59 PM
Let us know what happens by just changing the bolts. It will be enlightening to find out just how much of an improvement can be gained by just changing the bolts. I suspect though that it will take a combination of improvements to reach your goal.

Not sure if you are aware that there is a dedicated mill/drill group at Yahoo. A look there might help shed some light on this issue.

Here's the link... http://groups.yahoo.com/group/mill_drill/

lazlo
08-06-2008, 03:59 PM
The column can't be flexing that much. 4.5" OD cast iron with about 1/2 inch walls. Casting looks good on the inside.

Agreed. I've seen several posts, including Torker, where guys are filling their columns with concrete, but if you do the beam calculation on the 4.5" D column, there's no way it's the column that's flexing. I think it's the head clamp on the column (it's frightening when the head slips in a heavy cut), and the column base clamp to the mill base.


I think the bolts are a major factor here. (4) 16mm bolts hold the column to the base. They're marked "4.8". That's probably a tensile strength somewhere between cheddar cheese and talc. Even a good bolt that size will stretch a little. If I remove one of the 4 bolts, the total spindle deflection with approximately the same force goes from about .003 to about .005.

Same on mine. Basically all the bolts on the Mill/Drill are made of Chinese Cheese, so I replaced almost all of them with grade 8's, especially the two large head bolts* and the 4 base bolts. I also had a lot of crap (casting sand, paint, cosmolene, beer can slices, chicken parts, ...) under the column base, so cleaning that out not only gave a better mate between the mill base and the column base, but also made it much easier/consistent to tram.

*Grade 8's don't come that large, so I used the equivalent strength ASTM structural bolts. If you change these, note that you can't use the tire iron that comes with the Mill/Drill, so you need to get a large socket and wrench.

Just Bob Again
08-07-2008, 05:39 PM
Well, one bright idea down the drain. I replaced the base bolts. Cleaned off the sixteenth of an inch of Bondo that was under the bolt heads. Hoisted the column up and looked at the mating surface on the base. Nicely scraped and frosted. Unfortunately, also very warped despite the decoration. There was a big hump in the middle. Around 20 thou. I filed it flat and scraped at it a bit. Not surface-plate flat now, but at least it's bearing around the edges instead of rocking around the center. Torqued down the bolts with a big allen and a 5-pound sledge. No difference. I can still push the head maybe .002 and the quality of the cut is no better. I think the base must be flexing. It isn't real thick. Only maybe 3/8 inch.

Back to the drawing board.

BobWarfield
08-07-2008, 06:02 PM
hey, just bob, an idea from another bob. I am filling my mill base with epoxy granite. Easy to do and made the base much heavier and deader too. Details on my cnccookbook.com site.

As part of the process you may be able to engineer a more solid column to base connection.

Best,

BW

derekm
08-07-2008, 06:40 PM
Well, one bright idea down the drain. I replaced the base bolts. Cleaned off the sixteenth of an inch of Bondo that was under the bolt heads. Hoisted the column up and looked at the mating surface on the base. Nicely scraped and frosted. Unfortunately, also very warped despite the decoration. There was a big hump in the middle. Around 20 thou. I filed it flat and scraped at it a bit. Not surface-plate flat now, but at least it's bearing around the edges instead of rocking around the center. Torqued down the bolts with a big allen and a 5-pound sledge. No difference. I can still push the head maybe .002 and the quality of the cut is no better. I think the base must be flexing. It isn't real thick. Only maybe 3/8 inch.

Back to the drawing board.

heres a thought - put the dial gauge between the column and the base to see if you can detect the flex - might need a longish arm to the dial guage

lazlo
08-07-2008, 06:58 PM
There was a big hump in the middle. Around 20 thou. I filed it flat and scraped at it a bit. Not surface-plate flat now, but at least it's bearing around the edges instead of rocking around the center.

That's a big problem I've had with Chicom tools -- they tend not to stress relieve the cast iron before machining, so you often find weird warps/humps.

I had one of the Enco 5 1/2" Kurt clones, and the base was nicely milled flat, but unfortunately it warped by nearly 50 thou between machining and showing up on my doorstep. Took a lot of scraping to get it flat again, and then the bed was out of whack with the base.

But if you've got that much of a wobble on the base, I'd seriously consider taking it back, or asking for a replacement to be sent...

Just Bob Again
08-08-2008, 06:12 AM
[QUOTE=BobWarfield]hey, just bob, an idea from another bob. I am filling my mill base with epoxy granite. Easy to do and made the base much heavier and deader too. Details on my cnccookbook.com site./QUOTE]

I saw that granite epoxy article. Nice work. Unfortunately, I'm beginning to suspect that there's a crack in the base casting somewhere. That would explain that much flex. I put an indicator between the table and the base of the column. There's visible movement. About .003 total deflection when I push the head around. I'll check with Grizzly and see what they'll do. It's rather a pain to keep hoisting the machine up and down to play with it. I could take some heavy steel angle and sandwich it under the base using the mounting bolt holes. Just not sure if it's worth the effort.