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View Full Version : broke a gear in my headstock, got some questions



mtraven
08-18-2015, 02:06 PM
Hi all, I have a HF combo mill/lathe (44142) and recently broke some teeth of a gear inside the head stock. Specifically, the gear is 3rd inline on the gear train, that is, it runs off a compound gear that is driven by the gear on the spindle. HF no longer supports this unit in any way, the grizzly 9729 is identical & supported, but the part is out of stock until mid sept.

here is the gear:

https://lh3.googleusercontent.com/RLqfc2YxtCRnl47wNbZ7NKJfOGJkzS34XcOz1n-K-iU=w429-h572-no
https://lh3.googleusercontent.com/hneNCeMIpQVyKZj4dsgtLJsXJoHUOkkVau_gkddf34w=w763-h572-no

my questions:

1. why is it made in this manor (steel bore, plastic teeth)?

is it because its cheaper to cut teeth in plastic? Is it an intended failure point to prevent other damage? Is it to quiet the gear train?

2. what type of plastic might this be? I know nylon is common, this is pretty hard, maybe derlin? If I were to make one, what material would you recommend?

3. I have never cut a gear before, but what better time to learn than when you are in a bind? I dont have any gear cutting tools, but I do have a rotary table and or my lathe spindle. I was thinking I could grind a tool and use my lathe as a makeshift shaper to cut the teeth. I do not have proper indexing plates, but I'm thinking I might be able to make something to index off the old gear, perhaps spanning several teeth to get past the broken ones. Thoughts on this method?

thanks in advance for your help!

ps. if anyone is curious how it broke, I was attempting to cut a 1tpi tapered auger thread, driving the lathe manually by the leadscrew.

kf2qd
08-18-2015, 03:06 PM
The nylon gear has 2 purposes. It is the weak link. If it fails it does not tear out something more costly. A Nylon gear, and a straight cut one at that, will run much quieter than a metal gear. They probably used it more for to protect the gearbox than for the quiet.

You can lookup the Grizzly equivalent for your machine and get parts from them. Gear cutting will require a special cutter, and a good indexing head. You also need to use some different techniques with plastic as some plasitcs like to degas after they are machined and they shrink in cross section. Bores get bigger and the ODs get smaller...

You could also look for a metal gear, just take care not to over;load the whole machine...

Axkiker
08-18-2015, 03:42 PM
Does the mill portion still work ?? Or did this gear kill it

mtraven
08-18-2015, 03:55 PM
You can lookup the Grizzly equivalent for your machine and get parts from them. Gear cutting will require a special cutter, and a good indexing head. You also need to use some different techniques with plastic as some plasitcs like to degas after they are machined and they shrink in cross section. Bores get bigger and the ODs get smaller...

You could also look for a metal gear, just take care not to over;load the whole machine...

as stated in the original post, grizzly cant get me the gear for at least a month, having my lathe out of service for a month is just not acceptable. I will prob get one from them, but I need something to get me through to there.

as for the special gear cutter, I realize that I don't have the ideal tools, what is your opinion on the makeshift shaper method I described? still leaves me with an indexing problem to solve, but I have a few ideas brewing on that front.


" Does the mill portion still work ?? Or did this gear kill it "

gear kills the power feeds for both the lathe & mill, but both work in a manual capacity.

Zahnrad Kopf
08-18-2015, 04:10 PM
I have to Hob some 1.5Mod gears here shortly. If you can have all the other work DONE and READY, I might be able to help you out. You would need to have your blank completed and make an arbor for it as well. I would do ONLY the Hobbing.

Axkiker
08-18-2015, 04:35 PM
as stated in the original post, grizzly cant get me the gear for at least a month, having my lathe out of service for a month is just not acceptable. I will prob get one from them, but I need something to get me through to there.

as for the special gear cutter, I realize that I don't have the ideal tools, what is your opinion on the makeshift shaper method I described? still leaves me with an indexing problem to solve, but I have a few ideas brewing on that front.


" Does the mill portion still work ?? Or did this gear kill it "

gear kills the power feeds for both the lathe & mill, but both work in a manual capacity.


Well if your rotary table accepts plates I would just order one and go to town with a hand ground profile tool. Way back before I bought my indexing head I was in a similar position. I ended up grinding a profile tool by hand and used a makeshift doohicky to index off the old gear.

I think you can knock this out

ahidley
08-18-2015, 06:54 PM
I have the same machine and I also crashed it and blew the "fuse" that plastic gear. That's why you need spares. So make a few . I would take advantage of zahrands offer

oldtiffie
08-18-2015, 11:10 PM
Well if your rotary table accepts plates I would just order one and go to town with a hand ground profile tool. Way back before I bought my indexing head I was in a similar position. I ended up grinding a profile tool by hand and used a makeshift doohicky to index off the old gear.

I think you can knock this out

I think you will find that few if any "standard" "A", "B" or "C" plates have 127 holes so a plate for 127 holes would need to have 127 holes - but that would be "crowding it" if you wanted to stay within the limits of a standard set of sector arms.

PStechPaul
08-18-2015, 11:40 PM
It looks like this gear has 56 teeth. My lathe has an 80 tooth plastic gear that I stripped a while ago, but fortunately it came with a spare:

http://enginuitysystems.com/pix/tools/Lathe_Gears_1332_800p.jpg

I found some for sale on eBay, but I didn't need any. Here are some ABS gears that might work:
http://www.ebay.com/itm/65T-65Tooth-ABS-Change-Gear-7x10-7x12-Mini-Lathe-Harbor-Freight-Grizzly-/151235863094 (65 tooth)
http://www.ebay.com/itm/57T-57Tooth-ABS-Change-Gear-7x10-7x12-Mini-Lathe-Harbor-Freight-Grizzly/151235707592 (57 tooth)
http://www.ebay.com/itm/55T-55Tooth-ABS-Change-Gear-7x10-7x12-Mini-Lathe-Harbor-Freight-Grizzly-/161228264524 (http://www.ebay.com/itm/55T-55Tooth-ABS-Change-Gear-7x10-7x12-Mini-Lathe-Harbor-Freight-Grizzly-/161228264524?hash=item2589f4144c) (55 tooth)

The number of teeth may not matter much because it is just a "tumbler" or idler between the spindle gear and the small gear on the banjo.

http://enginuitysystems.com/pix/tools/Lathe_Gears_1163_800p.jpg

http://enginuitysystems.com/pix/tools/Lathe_Gears_0985_800p.jpg

mtraven
08-19-2015, 12:43 AM
It looks like this gear has 56 teeth. My lathe has an 80 tooth plastic gear that I stripped a while ago, but fortunately it came with a spare:

The number of teeth may not matter much because it is just a "tumbler" or idler between the spindle gear and the small gear on the banjo.


thanks for the suggestions, but mine is not a tumbler, its keyed to that shaft & outputs through 1 of 3 gears pinned to that shaft dependent on the position of the gear selector. so its got to be a direct match, 56t gear.

as for indexing plates, that's a no go, my table does not accept them, just quick indexing plates that are only good to about 32 divisions.

Zahnrad:
that is a very generous offer & I may end up taking you up on that. I'm working on a setup to try to do them on my own, Ill post at the end of the night & let you all know where I am at (or ask for more help).

Thank you all so much for your suggestions, its great to have this forum as a resource.

yf
08-19-2015, 03:23 AM
I can't remember where i saw this.
There is a way of making light duty non precision gears, by running a strip of heavy brass foil or thin sheet between any 2 gears of the correct
pitch. The strip will get corrugated, I believe that model outfits even sell this strip ready made in small sizes .
You cut off the amount of teeth you need and wrap it around a blank wheel and then pour in some alloy that then fills in the space between them.
Then center and bore the hole, keyway etc.

I've never done it, and don't know how much torque those teeth can transmit, but it shouldn't take too long to try.
If I was doing it I would drill some holes in the periphery of the blank to key in the molten alloy, no need for precise spacing.

Axkiker
08-19-2015, 09:12 AM
I think you will find that few if any "standard" "A", "B" or "C" plates have 127 holes so a plate for 127 holes would need to have 127 holes - but that would be "crowding it" if you wanted to stay within the limits of a standard set of sector arms.

I guess then im missing something here. Why would you need to have 127 holes? If the table has a 40:1 ratio you wouldnt need nearly 127 holes.

Maybe im just under the wrong impression that rotary tables have a 40:1 ratio????

chucketn
08-19-2015, 09:33 AM
So, you need a 56 tooth gear. Is it Mod 1 as are the 7x lathe change gears?

I ask, because I have built a digital indexer based on an Arduino which runs a driver/stepper connected to my 4" vertex RT. I have made straight hobbs for Mod 1 and 16 DP gears. Over the winter months I cut a set of change gears for a 12" Atlas lathe. I have not yet cut Mod 1 gears, but could.

Chuck

Zahnrad Kopf
08-19-2015, 11:11 AM
So, you need a 56 tooth gear. Is it Mod 1 as are the 7x lathe change gears?


I have to Hob some 1.5Mod gears here shortly. If you can have all the other work DONE and READY, I might be able to help you out.





I ask, because I have built a digital indexer based on an Arduino which runs a driver/stepper connected to my 4" vertex RT. I have made straight hobbs for Mod 1 and 16 DP gears. Over the winter months I cut a set of change gears for a 12" Atlas lathe. I have not yet cut Mod 1 gears, but could. Chuck

Well there's something one doesn't see every day. Hobs being made in a home shop environ. It happens. It's just not too common. How are you making your Hobs? Material? Heat Treat? Grinding? How are you relieving them? I am interested because it's a subject close to my heart due to the fact that I make a LOT of Non Standard Gears, bearing completely custom Pitches and Pressure Angles. Or are you actually making Form Mills, and not Hobs?

chucketn
08-19-2015, 12:54 PM
I first ground a HSS lathe tool to a precise fit in the gear tooth profile of the Mod or DP gear. I did this for both a 16 DPgear for the Atlas and a mod 1 gear for my own mini lathe.
Next I turned a 1/2" dia piece of drill rod to have 5 rings, spaced the same as a screw thread of the pitch of the gear. Like profiling a rack except the teeth were rings, not helical like a screw. I made one with each lathe tool, for each type of gear. I then gashed the rings into teeth with my mill, holding the drill rod with the RT in horizontal mode. Adjusting the RT to cut the gash and then relief. I don't have the resulting tool in front of me, but I think I cut 5 gashes, and relieved the backside of each tooth made. I also turned a relief(smaller dia for 1/4" between the 5th tooth and the shank on each tool.
I hardened the drill rod tools, but did not temper as I was cutting aluminum, and quenched in used motor oil.
I put the hardened tool in the mill, and mounted the gear blank on a mandrel in the RT, with the center ring of teeth set on the center axis of the blank. I used the Arduino based stepper setup on the RT to index the blank, made 2 passes to cut the gear profile to depth. The 1st, 2nd, 4th, and 5th ring of cutters each cut a partial profile, and the center or 3d ring of teeth cut to depth on one tooth at a time. As the RT was indexed, each ring of teeth on the cutter cut a little more of the involute profile. Obiously the complete gear was cut in 1 complete revolution, plus 3 teeth from the starting point.
As I cut a total of 8 gears for the atlas, I experimented with various depths of cut per pass, and making multiple passes at the same depth for a complete revolution of the blank. I settled on 2 passes per tooth, increment, 2 passes, as the quickest method for me.
I used WM Berg's Gear Spec program to calculate the gear blank diameter, and used formulas on the web to determine cut depth.

Chuck

chucketn
08-19-2015, 01:29 PM
I thought I had pictures of the gears I made for the Atlas and of the tool itself while I was making it as I would send pictures of the gears to the guy I was making them for. Can find them if I did.
I can take pics of the finished hobbs if needed.

Chuck

Zahnrad Kopf
08-19-2015, 01:32 PM
I first ground a HSS lathe tool to a precise fit in the gear tooth profile of the Mod or DP gear. < snip >

I used the Arduino based stepper setup on the RT to index the blank, made 2 passes to cut the gear profile to depth. The 1st, 2nd, 4th, and 5th ring of cutters each cut a partial profile, and the center or 3d ring of teeth cut to depth on one tooth at a time. As the RT was indexed, each ring of teeth on the cutter cut a little more of the involute profile. Obiously the complete gear was cut in 1 complete revolution, plus 3 teeth from the starting point.

Chuck

Ah. Okay. That is not a Hob. That is a Form Mill. You are cutting a Form. You are not generating Involutes. Huge difference and not a trivial or academic distinction. ( your efforts not withstanding )

chucketn
08-19-2015, 02:01 PM
Well, I'm not going to argue semantics. The gears I cut worked. just trying to show the OP that with a little study, and research, a working lathe, a rotary table and a mill, he can make a useable gear.
Cost, outside of the lathe, mill and RT was a few inches of 1/2" drill rod, some aluminum plate or large round for gear blanks( if you have a foundry you could cast the blanks from scrap, even beer and soda cans). All the theory and formulas are online, even the W.M. Berg program GearSpec was free. A lot of information was found by Google by searching on the term "Hobbing".

Chuck

PStechPaul
08-19-2015, 02:56 PM
The OP's gear appears to be mod 1.5. 56 teeth and an OD of 3.408" or 86mm would be 1.54 but the root diameter may be 84mm which is 1.5.

http://www.metrication.com/engineering/gears.html

ahidley
08-19-2015, 03:41 PM
Pstechpaul is correct. On my 44142 the change gears are module 1.0 and the gears that run in the oil bath are module 1.5, these include the plastic toothed ones.

ahidley
08-19-2015, 03:45 PM
Also for those not paying attention. I bet that oldtiffie posted in the wrong thread. There is another thread inquiring about 127 tooth gears being made. FWIW

rythmnbls
08-19-2015, 03:52 PM
I think Zahnrad Kopf is talking about making a hobb like in this video and using it to generate teeth. This is something I'd like to try one day.

https://www.youtube.com/watch?v=kJ8kyC_bpHs

Steve.

Zahnrad Kopf
08-19-2015, 10:17 PM
I think Zahnrad Kopf is talking about making a hobb like in this video and using it to generate teeth. This is something I'd like to try one day.
https://www.youtube.com/watch?v=kJ8kyC_bpHs
Steve.

Those and those similar to those, yes. I have no desire to argue with Chuck. I simply, personally feel it is important to not only refer to things by their proper name, but take the care to do so when conversing with others about it on public forums. It's of some importance to remember that some others come to these forums to learn. Blithely distributing incorrect information doesn't serve anyone well.

I do realize that the majority of participants here in this specific forum are of the home user/hobby shop segment but I don't think they'd knowingly choose to learn something incorrectly, whether by ignorance, laziness, or whatever the reason. Fact of the matter is that Chuck's mill bears no difference to stacking five Involute Mills, one atop of another. Plain, and simple.

That does not detract from his work or the utility of it, to him. It seems to have been made well enough for his requirements, and I applaud his efforts and work, but it is not a Hob in any stretch of the imagination. The distinction is immensely important not for any semantic. Rather it is important for the same reason we do not call a drill press a milling machine simply because someone stuck an end mill in the chuck, lacking actual proper equipment.


Hobs have flat flanks and flat tips. They rotate in synchronization with the gear blank being cut. They accurately generate Involutes. They can manufacture ANY number of tooth gear within that Pitch they are made for.

Form Mills have an approximation of the tooth space shape. The blank is held stationary while the Form Mill addresses it. The Form Mill can cut only the shape that its volume defines when used in typical purpose. Form Mills are useful for very small ranges of tooth numbers within the Pitch they are made for.


It is not the difference between to-MAY-toe and to-MAH-toe. It's the difference between a potato and a rutabega.

Zahnrad Kopf
08-19-2015, 10:36 PM
Zahnrad:
that is a very generous offer & I may end up taking you up on that. I'm working on a setup to try to do them on my own, Ill post at the end of the night & let you all know where I am at (or ask for more help).

I'll be Hobbing them late next week, it looks like. Let me know if you'll want to go that route. You can email me directly through the forum. For the sake of clarity, this would be Hobbed free of charge, provided that you provide everything ready to go. I figure being in Chicago you've suffered a bit overmuch already... :)

mtraven
08-20-2015, 07:45 AM
ok, I have not read any of your replies in the last 24 hours, I intend to and will reply accordingly, but I have been hard at work solving this problem. I am happy to report that I have successfully cut a replacement gear(my very first gear!!) & installed it, so far it seems to be functioning well. note the material is UHMW, not by choice, just what I had around to test out my gear cutting process. I intend to get some nylon or derlin to cut a permanent replacement, but I figured I see how this one holds up. So here's how I did it and the result:

I set up a makeshift shaper / broaching operation on the lathe using the carriage for the liner motion & the compound to advance cutting depth, bottoming out at full depth giving me a hard stop.

I ground a hss tool to fit the profile of the teeth, the tip of the tool could have been shaped a little better, but overall is was an acceptable match.

for indexing, I used the old gear & ran the tool into each tooth to set the rotational position. I needed a way to lock that position, so I made a spindle lock:

https://lh3.googleusercontent.com/59W_1SpYftMauAIcDK8rYO8Q3cQFkD5gsTWa4SiOrbU=w763-h572-no
https://lh3.googleusercontent.com/JjNa5JOOPTCOtyrgeDastykQTxBsjqjCaQZnSaHLPLg=w763-h572-no

here is the gear cutting setup:
https://lh3.googleusercontent.com/jDMGAhSMHV1dbaNeglQ0udO86QUmheWmdj-1cVMOUFo=w763-h572-no

finished cutting teeth:
https://lh3.googleusercontent.com/1R9p2813m_hVUMi-wy0tscq1KEkE7L16Y73us94LN3I=w763-h572-no

mtraven
08-20-2015, 07:46 AM
little bit of welding & machining to make the steel bore and we have a finished gear:
https://lh3.googleusercontent.com/Rje8ULVgx0m79WOzsgf2X9whslC07kIoHx1Ui6_veDQ=w763-h572-no

I did try to cut the keyway using the shaper method I used for the teeth, but steel proved too strong. I resorted to tiny files, which sucked, but worked.

new gear reinstalled:
https://lh3.googleusercontent.com/nRL7IZlLtmWZ3I0Zm1xPkacCEBHkPoLUf1i-hXKHeGc=w429-h572-no


I gotta say, this one gave me an extra special sense of accomplishment having been my first gear & fixing a lathe crippling problem. Thanks for your advice & encouragement

chucketn
08-20-2015, 08:05 AM
I gotta say, this one gave me an extra special sense of accomplishment having been my first gear & fixing a lathe crippling problem. Thanks for your advice & encouragement

Well done! What ever you want to call the process...

Chuck

ahidley
08-20-2015, 01:11 PM
How did you attach the plastic to the steel?

Zahnrad Kopf
08-20-2015, 01:32 PM
Absolutely love your spindle brake/clamp! Well done. :)

mtraven
08-20-2015, 03:24 PM
How did you attach the plastic to the steel?

steel disc sits in a registration so center it & keep it flush. (6) #8-32 screws threaded into the steel & perm. locktite for safe keeping.


Absolutely love your spindle brake/clamp! Well done. :)

thank you! can you tell I made that disk out of an old cast iron weight lifting plate?
here is a couple photos of it coming to be:
https://lh3.googleusercontent.com/k_73aePiqCak18SdzmD5KtK55of1hIjNHpNC5jnD-a8=w763-h572-no
https://lh3.googleusercontent.com/BTpPbCdSSpgdkdZFqaLKAUvby05dSeJ7flg1_s-HV5s=w763-h572-no
https://lh3.googleusercontent.com/x_KAD9OfwmHRAakWVPrBze4v1g9RgNK-i6HqkDJORh4=w763-h572-no


interesting that you call it a brake, I know nicer machines often have an emergency brake and that's what I intend to do with mine. Something like a little brake caliper hydraulically or cable linked to foot pedal. also might pop some basic bolt circles in it for simple indexing.

PStechPaul
08-20-2015, 03:28 PM
The tooth profile is probably not quite correct, but for a plastic gear, it will probably work just fine and it may even deform to match the profile of the mating steel gears. I have wondered if it is possible to use a heated metal gear to form a mating plastic gear once it has already been gashed with the correct tooth count and spacing. It would need to be a thermoplastic (https://en.wikipedia.org/wiki/Thermoplastic) material, which can be ABS, acrylic, nylon, PLA, polycarbonate, polyethylene, polypropylene, polystyrene, or PVC. Some of these are better than others for various reasons, and the temperature is probably somewhat critical.

Good job on the makeshift gearcutter. :)

mtraven
08-20-2015, 03:40 PM
ahidley:

I tried to pm this message to you, but it says your inbox is full.....

I have actually never talked to anyone else who owns this machine, I am curious what you think of it? I have spent a lot of time rebuilding the lathe parts making it a reasonable machine. Have you done anything to improve yours?

I find the mill almost completely useless, you?

--matt

mtraven
08-20-2015, 03:50 PM
The tooth profile is probably not quite correct, but for a plastic gear, it will probably work just fine and it may even deform to match the profile of the mating steel gears. I have wondered if it is possible to use a heated metal gear to form a mating plastic gear once it has already been gashed with the correct tooth count and spacing. It would need to be a thermoplastic (https://en.wikipedia.org/wiki/Thermoplastic) material, which can be ABS, acrylic, nylon, PLA, polycarbonate, polyethylene, polypropylene, polystyrene, or PVC. Some of these are better than others for various reasons, and the temperature is probably somewhat critical.
Good job on the makeshift gearcutter. :)

you are spot on that the profile is not exactly right, I think I got the side angles good, but the bottom of the teeth is more of a "v" than the "u" in the original gear. It feels really good in the gear box & is actually a touch quieter than the original.

An interesting note, the profile was almost exactly the same as an acme threading tool, which is what I used as a starting point. I always have difficulty grinding the flat at the tip without butchering the whole thing.

the thermo-forming concept seems quite interesting, and would be versatile to make 1-off gears when ya need them. I know people have used a similar method to form leadscrew nuts in derlin, with a pretty high degree of success. if you ever try that, let me know!

ahidley
08-20-2015, 04:43 PM
Mtraven. It's a cheap light duty machine. I don't allow people in the shop. But they see what comes out and are impressed. The 3/4 hp motors SUCK. After three replacements =five motors. I threw them to the side and went with VIDs driving 1.5 hp three phase motors. That was a thousand percent improvement. It seemed like the 3/4 hp were causing the machine to vibrate and it was impossible to hold an acceptable tolerance because everything was flexing. With the 1.5 hp three phase is runs SOOOOOO SMOOOOOOTH. on the lathe. I can now run depth of cut at .040 in steel about. Two inches in diameter. With the mill I can run depth of cut at .030 with a two inche diameter mill with four inserts cutting steel. I also added a digital readout for x and y. I kept screwing up they y between the mill and lathe. Using the lathe you have to divide. By two. I've added tumble gears to it make lefthand threads. Thanks Pstechpaul.

ahidley
08-20-2015, 04:54 PM
Made backplates for eight inch three jaw chucks, eight inch four jaw independent and not independNt. Eight inch six jaw chuck as well as a 5c chuck . I've turned flywheels down from big block chevys. They. Are sixteen inches in diameter. Most shops couldn't do it due to the large diameter.
I had a guy from the well drillers come with a six inch drill bit retrieval tool that he wanted turned down .080 . That tool weighed about two hundred pounds and required me to make a sixteen inch extension to the ways so I could use the tailstock.

ahidley
08-20-2015, 05:06 PM
I've Made dozens of gears. I bought a set of module 1.0 & 1.5 gear cutters awhile ago after finding out that harbor freight has no more parts.
I've lost count to the number of jetski drive shafts I've made for the unlimited class. These are basically one inch diameter stainless shafts with splines on both ends caring 175 hp. They have gone to the jetski worlds at lake havazue .az. all in all its a perfectly capable machine just be easy on it and stay within its means and it'll. Serve you well

ahidley
08-20-2015, 05:11 PM
Sorry the spell checker on this phone us screwing up my grammar.

ahidley
08-20-2015, 05:14 PM
Also my mailbox is NOT full. There can't be more than five messages in the inbox. George please. Repair. The broken mailbox issue

George Bulliss
08-20-2015, 06:41 PM
Also my mailbox is NOT full. There can't be more than five messages in the inbox. George please. Repair. The broken mailbox issue

I'll look into it tomorrow AM when I get back to the office. I'm somewhat limited in what I can do with PMs but will coordinate with you to get it fixed.

mattthemuppet
08-20-2015, 07:16 PM
whoa, way to go Matt, that is seriously impressive. Obviously, one wouldn't expect anything less from someone called Matt :)

mtraven
08-22-2015, 03:38 PM
hey chuck-

having problems sending you a pm in response to yours, so I hope you see this:

Thanks Chuck, that's all very helpful and encourages me to try it out. What was the difficulty in coupling the motor to the table?

my email is mtraven@gmail.com if you wanted to send any pics, that be great.

-matt